Lokalized

Lokalized facilitates natural-sounding software translations on the JVM.

It is both a file format…

{
  "I read {{bookCount}} books." : {
    "translation" : "I read {{bookCount}} {{books}}.",    
    "placeholders" : {
      "books" : {
        "value" : "bookCount",
        "translations" : {
          "CARDINALITY_ONE" : "book",
          "CARDINALITY_OTHER" : "books"
        }
      }
    },
    "alternatives" : [
      {
        "bookCount == 0" : "I didn't read any books."        
      }
    ]
  }  
}

…and a library that operates on it.

String translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 0);
  }});
 
assertEquals("I didn't read any books.", translation);

Design Goals

Design Non-Goals

Roadmap

License

Apache 2.0

Maven Installation

<dependency>
  <groupId>com.lokalized</groupId>
  <artifactId>lokalized-java</artifactId>
  <version>1.0.1</version>
</dependency>

Direct Download

If you don’t use Maven, you can drop lokalized-java-1.0.1.jar directly into your project. No other dependencies are required.

Why Lokalized?

Perhaps most importantly, the Lokalized placeholder system and expression language allow you to support edge cases that are critical to natural-sounding translations - this can be difficult to achieve using traditional solutions.

Getting Started

We’ll start with hands-on examples to illustrate key features.

1. Create Localized Strings Files

Filenames must conform to the IETF BCP 47 language tag format.

Here is a generic English (en) localized strings file which handles two localizations:

{
  "I am going on vacation" : "I am going on vacation.",
  "I read {{bookCount}} books." : {
    "translation" : "I read {{bookCount}} {{books}}.",    
    "placeholders" : {
      "books" : {
        "value" : "bookCount",
        "translations" : {
          "CARDINALITY_ONE" : "book",
          "CARDINALITY_OTHER" : "books"
        }
      }
    },
    "alternatives" : [
      {
        "bookCount == 0" : "I didn't read any books."        
      }
    ]
  }  
}

Here is a British English (en-GB) localized strings file:

{
  "I am going on vacation." : "I am going on holiday."
}

Lokalized performs locale matching and falls back to less-specific locales as appropriate, so there is no need to duplicate all the en translations in en-GB - it is sufficient to specify only the dialect-specific differences.

2. Create a Strings Instance

// Your "native" fallback strings file, used in case no specific locale match is found. 
// ISO 639 alpha-2 or alpha-3 language code 
final String FALLBACK_LANGUAGE_CODE = "en";
 
// Creates a Strings instance which loads localized strings files from the given directory. 
// Normally you'll only need a single shared instance to support your entire application, 
// even for multitenant/concurrent usage, e.g. a Servlet container 
Strings strings = new DefaultStrings.Builder(FALLBACK_LANGUAGE_CODE,
    () -> LocalizedStringLoader.loadFromFilesystem(Paths.get("my/strings/directory")))
  .build();

You may also provide the builder with a locale-supplying lambda, which is useful for environments like webapps where each request can have a different locale.

// "Smart" locale selection which queries the current web request for locale data. 
// MyWebContext is a class you might write yourself, perhaps using a ThreadLocal internally 
Strings webappStrings = new DefaultStrings.Builder(FALLBACK_LANGUAGE_CODE,
    () -> LocalizedStringLoader.loadFromFilesystem(Paths.get("my/strings/directory")))
  .localeSupplier(() -> MyWebContext.getHttpServletRequest().getLocale())
  .build();

3. Ask Strings Instance For Translations

// Lokalized knows how to map numbers to plural cardinalities per locale. 
// That is, it understands that 3 means CARDINALITY_OTHER ("books") in English 
String translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 3);
  }});
 
assertEquals("I read 3 books.", translation);
 
// 1 means CARDINALITY_ONE ("book") in English 
translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 1);
  }});
 
assertEquals("I read 1 book.", translation);
 
// A special alternative rule is applied when bookCount == 0 
translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 0);
  }});
 
assertEquals("I didn't read any books.", translation);
 
// Here we force British English. 
// Note that providing an explicit locale is an uncommon use case - 
// standard practice is to specify a localeSupplier when constructing your  
// Strings instance and Lokalized will use it to pick the appropriate locale, e.g.  
// the locale specified by the current web request's Accept-Language header 
translation = strings.get("I am going on vacation.", Locale.forLanguageTag("en-GB"));
 
// We have an exact match for this key in the en-GB file, so that translation is applied. 
// If none were found, we would fall back to "en" and try there instead 
assertEquals("I am going on holiday.", translation);

A More Complex Example

Lokalized’s strength is handling phrases that must be rewritten in different ways according to language rules. Suppose we introduce gender alongside plural forms. In English, a noun’s gender usually does not alter other components of a phrase. But in Spanish it does.

This English statement has 4 variants:

In Spanish, we have the same number of variants (in a language like Russian or Arabic there would be more!) But notice how the statements must change to match gender - uno becomes una, jugadores becomes jugadoras, etc.

English Translation File

English is a little simpler than Spanish because gender only affects the He or She component of the sentence.

{
  "{{heOrShe}} was one of the {{groupSize}} best baseball players." : {
    "translation" : "{{heOrShe}} was one of the {{groupSize}} best baseball players.",
    "placeholders" : {
      "heOrShe" : {
        "value" : "heOrShe",
        "translations" : {
          "MASCULINE" : "He",
          "FEMININE" : "She"
        }
      }
    },
    "alternatives" : [
      {
        "heOrShe == MASCULINE && groupSize <= 1" : "He was the best baseball player."        
      },
      {
        "heOrShe == FEMININE && groupSize <= 1" : "She was the best baseball player."        
      }
    ]
  }
}

Spanish Translation File

Note that we define our own placeholders in translation and drive them off of the heOrShe value to support gender-based word changes.

{
  "{{heOrShe}} was one of the {{groupSize}} best baseball players." : {
    "translation" : "Fue {{uno}} de {{los}} {{groupSize}} mejores {{jugadores}} de béisbol.",
    "placeholders" : {
      "uno" : {
        "value" : "heOrShe",
        "translations" : {
          "MASCULINE" : "uno",
          "FEMININE" : "una"
        }
      },
      "los" : {
        "value" : "heOrShe",
        "translations" : {
          "MASCULINE" : "los",
          "FEMININE" : "las"
        }
      },
      "jugadores" : {
        "value" : "heOrShe",
        "translations" : {
          "MASCULINE" : "jugadores",
          "FEMININE" : "jugadoras"
        }
      }
    },
    "alternatives" : [
      {
        "heOrShe == MASCULINE && groupSize <= 1" : "Él era el mejor jugador de béisbol."        
      },
      {
        "heOrShe == FEMININE && groupSize <= 1" : "Ella era la mejor jugadora de béisbol."        
      }
    ]
  }
}

The Rules, Exercised

Again, we keep the gender and plural logic out of our code entirely and leave rule processing to the translation configuration.

// "Normal" translation 
translation = strings.get("{{heOrShe}} was one of the {{groupSize}} best baseball players.",
  new HashMap<StringObject>() {{
    put("heOrShe", Gender.MASCULINE);
    put("groupSize", 10);
  }});
 
assertEquals("He was one of the 10 best baseball players.", translation);
 
// Alternative expression triggered 
translation = strings.get("{{heOrShe}} was one of the {{groupSize}} best baseball players.",
  new HashMap<StringObject>() {{
    put("heOrShe", Gender.MASCULINE);
    put("groupSize", 1);
  }});
 
assertEquals("He was the best baseball player.", translation);
 
// Let's try Spanish 
translation = strings.get("{{heOrShe}} was one of the {{groupSize}} best baseball players.",
  new HashMap<StringObject>() {{
    put("heOrShe", Gender.FEMININE);
    put("groupSize", 3);
  }}, Locale.forLanguageTag("es"));
 
// Note that the correct feminine forms were applied 
assertEquals("Fue una de las 3 mejores jugadoras de béisbol.", translation);

Recursive Alternatives

You can exploit the recursive nature of alternative expressions to reduce logic duplication. Here, we define a toplevel alternative for groupSize <= 1 which itself has alternatives for MASCULINE and FEMININE cases. This is equivalent to the alternative rules defined above but might be a more “comfortable” way to express behavior for some.

Note that this is just a snippet to illustrate functionality - the other portion of this localized string has been elided for brevity.

{
  "alternatives" : [
    {
      "groupSize <= 1" : {
        "alternatives" : [
          {
            "heOrShe == MASCULINE" : "Él era el mejor jugador de béisbol."
          },
          {
            "heOrShe == FEMININE" : "Ella era la mejor jugadora de béisbol."
          }
        ]
      }
    }
  ]
}

A Cardinality Range Example

When expressing a range of values (1-3 meters, 2.5-3.5 hours), the cardinality of the range is determined by applying per-language rules to its start and end cardinalities.

In English we don’t think about this - all ranges are of the form CARDINALITY_OTHER - but many other languages have range-specific forms.

French Translation File

French ranges can be either CARDINALITY_ONE or CARDINALITY_OTHER.

{
  "The meeting will be {{minHours}}-{{maxHours}} hours long." : {
    "translation" : "La réunion aura une durée de {{minHours}} à {{maxHours}} {{heures}}.",
    "placeholders" : {
      "heures" : {
        "range" : {
          "start" : "minHours",
          "end" : "maxHours"
        },
        "translations" : {
          "CARDINALITY_ONE" : "heure",
          "CARDINALITY_OTHER" : "heures"
        }
      }
    }
  }
}

English Translation File

All English range forms evaluate to CARDINALITY_OTHER so the file can be kept simple.

{
  "The meeting will be {{minHours}}-{{maxHours}} hours long." : "The meeting will be {{minHours}}-{{maxHours}} hours long."
}

Cardinality Ranges, Exercised

// French CARDINALITY_OTHER case  
String translation = strings.get("The meeting will be {{minHours}}-{{maxHours}} hours long.",
  new HashMap<StringObject>() {{
    put("minHours", 1);
    put("maxHours", 3);
  }}, Locale.forLanguageTag("fr"));
 
assertEquals("La réunion aura une durée de 1 à 3 heures.", translation);
 
// French CARDINALITY_ONE case 
translation = strings.get("The meeting will be {{minHours}}-{{maxHours}} hours long.",
  new HashMap<StringObject>() {{
    put("minHours", 0);
    put("maxHours", 1);
  }}, Locale.forLanguageTag("fr"));
 
assertEquals("La réunion aura une durée de 0 à 1 heure.", translation);

An Ordinality Example

Many languages have special forms called ordinals to express a “ranking” in a sequence of numbers. For example, in English we might say

Let’s look at an example related to birthdays.

English Translation File

English has 4 ordinals.

{
  "{{hisOrHer}} {{year}}th birthday party is next week." : {  
    "translation" : "{{hisOrHer}} {{year}}{{ordinal}} birthday party is next week.",
    "placeholders" : {  
      "hisOrHer" : {  
        "value" : "hisOrHer",
        "translations" : {  
          "MASCULINE" : "His",
          "FEMININE" : "Her"
        }
      },
      "ordinal" : {  
        "value" : "year",
        "translations" : {  
          "ORDINALITY_ONE" : "st",
          "ORDINALITY_TWO" : "nd",
          "ORDINALITY_FEW" : "rd",
          "ORDINALITY_OTHER" : "th"
        }
      }
    }
  }
}

Spanish Translation File

Spanish doesn’t have ordinals, so we can disregard them. But we do have a few special cases - a first birthday and a quinceañera for girls.

{
  "{{hisOrHer}} {{year}}th birthday party is next week." : {
    "translation" : "Su fiesta de cumpleaños número {{year}} es la próxima semana.",
    "alternatives" : [
      {
        "year == 1" : "Su primera fiesta de cumpleaños es la próxima semana."        
      },
      {
        "hisOrHer == FEMININE && year == 15" : "Su quinceañera es la próxima semana."        
      }
    ]
  }
}

Ordinals, Exercised

translation = strings.get("{{hisOrHer}} {{year}}th birthday party is next week.",
  new HashMap<StringObject>() {{
    put("hisOrHer", Gender.MASCULINE);
    put("year", 18);
  }});
 
// The ORDINALITY_OTHER rule is applied for 18 in English 
assertEquals("His 18th birthday party is next week.", translation);
 
translation = strings.get("{{hisOrHer}} {{year}}th birthday party is next week.",
  new HashMap<StringObject>() {{
    put("hisOrHer", Gender.FEMININE);
    put("year", 21);
  }});
 
// The ORDINALITY_ONE rule is applied to any of the "one" numbers (1, 11, 21, ...) in English 
assertEquals("Her 21st birthday party is next week.", translation);
 
translation = strings.get("{{hisOrHer}} {{year}}th birthday party is next week.",
  new HashMap<StringObject>() {{
    put("hisOrHer", Gender.MASCULINE);
    put("year", 18);
  }}, Locale.forLanguageTag("es"));
 
// Normal case 
assertEquals("Su fiesta de cumpleaños número 18 es la próxima semana.", translation);
 
translation = strings.get("{{hisOrHer}} {{year}}th birthday party is next week.",
  new HashMap<StringObject>() {{
    put("year", 1);
  }}, Locale.forLanguageTag("es"));
 
// Special case for first birthday 
assertEquals("Su primera fiesta de cumpleaños es la próxima semana.", translation);
 
translation = strings.get("{{hisOrHer}} {{year}}th birthday party is next week.",
  new HashMap<StringObject>() {{
    put("hisOrHer", Gender.FEMININE);
    put("year", 15);
  }}, Locale.forLanguageTag("es"));
 
// Special case for a girl's 15th birthday 
assertEquals("Su quinceañera es la próxima semana.", translation);

Language Forms

Gender

Gender rules vary across languages, but the general meaning is the same.

Lokalized supports these values:

Lokalized provides a Gender type which enumerates supported genders.

Plural Cardinality

For example: 1 book, 2 books, ...

Plural rules vary widely across languages.

Lokalized supports these values according to CLDR rules:

Values do not necessarily map exactly to the named number, e.g. in some languages CARDINALITY_ONE might mean any number ending in 1, not just 1. Most languages only support a few plural forms, some have none at all (represented by CARDINALITY_OTHER in those cases).

Japanese
English
Russian

Lokalized provides a Cardinality type which encapsulates cardinal functionality.

You may programmatically determine cardinality using Cardinality#forNumber(Number number, Locale locale) and Cardinality#forNumber(Number number, Integer visibleDecimalPlaces, Locale locale) as shown below.

It is important to note that the number of visible decimal places can be important for some languages when performing cardinality evaluation. For example, in English, 1 matches CARDINALITY_ONE but 1.0 matches CARDINALITY_OTHER. Even though the numbers’ true values are identical, you would say 1 inch and 1.0 inches and therefore must take visible decimals into account.

// Basic case - a primitive number, no decimals 
Cardinality cardinality = Cardinality.forNumber(1, Locale.forLanguageTag("en"));
assertEquals(Cardinality.ONE, cardinality);
 
// In the absence of an explicit number of visible decimals, 
// 1.0 evaluates to Cardinality.ONE since primitive 1 == primitive 1.0 
cardinality = Cardinality.forNumber(1.0, Locale.forLanguageTag("en"));
assertEquals(Cardinality.ONE, cardinality);
 
// With 1 visible decimal specified ("1.0"), we evaluate to Cardinality.OTHER 
cardinality = Cardinality.forNumber(1, 1, Locale.forLanguageTag("en"));
assertEquals(Cardinality.OTHER, cardinality);
 
// Let's try BigDecimal instead of a primitive... 
cardinality = Cardinality.forNumber(new BigDecimal("1"), Locale.forLanguageTag("en"));
assertEquals(Cardinality.ONE, cardinality);
 
// Using BigDecimal obviates the need to specify visible decimals 
// since they can be encoded directly in the number. 
// We evaluate to Cardinality.OTHER, as expected 
cardinality = Cardinality.forNumber(new BigDecimal("1.0"), Locale.forLanguageTag("en"));
assertEquals(Cardinality.OTHER, cardinality);

Plural Cardinality Ranges

For example: 0-1 hours, 1-2 hours, ...

The plural form of the range is determined by examining the cardinality of its start and end components.

English
French
Latvian

You may programmatically determine a range’s cardinality using Cardinality#forRange(Cardinality start, Cardinality end, Locale locale) as shown below.

// Latvian has a number of interesting range rules. 
// ZERO-ZERO -> OTHER 
Cardinality cardinality = Cardinality.forRange(Cardinality.ZERO, Cardinality.ZERO, Locale.forLanguageTag("lv"));
assertEquals(Cardinality.OTHER, cardinality);
 
// ZERO-ONE -> ONE 
cardinality = Cardinality.forRange(Cardinality.ZERO, Cardinality.ONE, Locale.forLanguageTag("lv"));
assertEquals(Cardinality.ONE, cardinality);

Ordinals

For example: 1st, 2nd, 3rd, 4th, ...

Similar to plural cardinality, ordinal rules very widely across languages.

Lokalized supports these values according to CLDR rules:

Again, like cardinal values, ordinals do not necessarily map to the named number. For example, ORDINALITY_ONE might apply to any number that ends in 1.

Spanish
English
Italian

Lokalized provides an Ordinality type which encapsulates ordinal functionality.

You may programmatically determine ordinality using Ordinality#forNumber(Number number, Locale locale) as shown below.

// e.g. "1st" 
Ordinality ordinality = Ordinality.forNumber(1, Locale.forLanguageTag("en"));
assertEquals(Ordinality.ONE, ordinality);
 
// e.g. "2nd" 
ordinality = Ordinality.forNumber(2, Locale.forLanguageTag("en"));
assertEquals(Ordinality.TWO, ordinality);
 
// e.g. "3rd" 
ordinality = Ordinality.forNumber(3, Locale.forLanguageTag("en"));
assertEquals(Ordinality.FEW, ordinality);
 
// e.g. "21st" 
ordinality = Ordinality.forNumber(21, Locale.forLanguageTag("en"));
assertEquals(Ordinality.ONE, ordinality);
 
// e.g. "27th" 
ordinality = Ordinality.forNumber(27, Locale.forLanguageTag("en"));
assertEquals(Ordinality.OTHER, ordinality);

Localized Strings File Format

Structure

With formalities out of the way, let’s return to our example en-GB strings file, which contains a single translation. We can use the string form shorthand to concisely express our intent:

{
  "I am going on vacation." : "I am going on holiday."
}

This is equivalent to the more verbose object form, which we don’t need in this situation.

{
  "I am going on vacation." : {
    "translation" : "I am going on holiday."
  }
}

In addition to translation, each object form supports 3 additional keys: commentary, placeholders, and alternatives.

All 4 are optional, with the stipulation that you must provide either a translation or at least one alternatives value.

Commentary

This free-form field is used to supply context for the translator, such as how and where the phrase is used in the application. It might also include documentation about the application-supplied placeholder values (names and types) so it’s clear what data is available to perform the translation.

{
  "I am going on vacation." : {
    "commentary" : "This is one of the options in the user's status update dropdown.",
    "translation" : "I am going on holiday."
  }
}

Placeholders

A placeholder is any translation value enclosed in a pair of “mustaches” - {{PLACEHOLDER_NAME_HERE}}.

You are free to add as many as you like to support your translation.

Placeholder values are initially specified by application code - they are the context that is passed in at string evaluation time.

Your translation file may override passed-in placeholders if desired, but that is an uncommon use case.

In the below example of an en strings file, the application code provides the bookCount value and the translation file introduces a books value to aid final translation.

{
  "I read {{bookCount}} books." : {
    "translation" : "I read {{bookCount}} {{books}}.",    
    "placeholders" : {
      "books" : {
        "value" : "bookCount",
        "translations" : {
          "CARDINALITY_ONE" : "book",
          "CARDINALITY_OTHER" : "books"
        }
      }
    }
  }  
}

Each placeholders object key is the name of the placeholder - books, in this example - and the value is an object with value and translations.

Here, the value of bookCount is evaluated against the specified cardinality rules and the result is placed into books. For example, if application code passes in 1 for bookCount, this matches CARDINALITY_ONE and book is the value of the books placeholder. If application code passes in a different value, CARDINALITY_OTHER is matched and books is used.

Supported values for translations are Cardinality, Ordinality, and Gender types.

You may not mix language forms in the same translations object. For example, it is illegal to specify both CARDINALITY_ONE and GENDER_MASCULINE.

The placeholder structure is slightly different for cardinality ranges. A range property is introduced and requires both a start and end value.

{
  "The meeting will be {{minHours}}-{{maxHours}} hours long." : {
    "translation" : "La réunion aura une durée de {{minHours}} à {{maxHours}} {{heures}}.",
    "placeholders" : {
      "heures" : {
        "range" : {
          "start" : "minHours",
          "end" : "maxHours"
        },
        "translations" : {
          "CARDINALITY_ONE" : "heure",
          "CARDINALITY_OTHER" : "heures"
        }
      }
    }
  }
}

Here, the cardinalities of minHours and maxHours are evaluated to determine the overall cardinality of the range, which is used to select the appropriate value in translations.

You are prohibited from supplying both range and value fields - use range only for cardinality ranges and value otherwise.

Alternatives

You may specify parenthesized expressions of arbitrary complexity in alternatives to fine-tune your translations. It’s perfectly legal to have an alternative like this:

gender == MASCULINE && (bookCount > 10 || magazineCount > 20)

Lokalized will automatically evaluate cardinality and ordinality for numbers if required by the expression. For example, in English, if I were to supply bookCount of 50, this expression would evalute to true:

bookCount == CARDINALITY_OTHER

…and so would this:

bookCount == 50

Note that the supported comparison operators for cardinality, ordinality, and gender forms are == and !=. You cannot say bookCount < CARDINALITY_FEW, for example.

Alternative expression recursion is supported. That is, each value for alternatives can itself have translation, placeholders, commentary, and alternatives. You can also use the simpler string-only form if no special translation functionality is needed.

Alternative evaluation follows these rules:

A somewhat contrived example of multiple levels of recursion follows. The first level of recursion uses a full object, the second uses the string shorthand.

{
  "I read {{bookCount}} books." : {
    "translation" : "I read {{bookCount}} books.",    
    "alternatives" : [
      {
        "bookCount < 3" : {
          "translation" : "I only read a few books. {{bookCount}}, in fact!",
          "alternatives": [
            {
              "bookCount == 0" : "I'm ashamed to admit I didn't read anything."
            }
          ]
        }        
      }
    ]
  }  
}

Evaluation works as you might expect.

// Deepest recursion 
String translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 0);
  }});
 
assertEquals("I'm ashamed to admit I didn't read anything.", translation);
 
// 1 level deep recursion 
translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 1);
  }});
 
assertEquals("I only read a few books. 1, in fact!", translation);
 
// Normal case 
translation = strings.get("I read {{bookCount}} books.",
  new HashMap<StringObject>() {{
    put("bookCount", 3);
  }});
 
assertEquals("I read 3 books.", translation);

A grammar for alternative expressions follows.

EXPRESSION = OPERAND COMPARISON_OPERATOR OPERAND | "(" EXPRESSION ")" | EXPRESSION BOOLEAN_OPERATOR EXPRESSION ;
OPERAND = VARIABLE | LANGUAGE_FORM | NUMBER ;
LANGUAGE_FORM = CARDINALITY | ORDINALITY | GENDER ;
CARDINALITY = "CARDINALITY_ZERO" | "CARDINALITY_ONE" | "CARDINALITY_TWO" | "CARDINALITY_FEW" | "CARDINALITY_MANY" | "CARDINALITY_OTHER" ;
ORDINALITY = "ORDINALITY_ZERO" | "ORDINALITY_ONE" | "ORDINALITY_TWO" | "ORDINALITY_FEW" | "ORDINALITY_MANY" | "ORDINALITY_OTHER" ;
GENDER = "MASCULINE" | "FEMININE" | "NEUTER" ;
VARIABLE = { alphabetic character | digit } ;
BOOLEAN_OPERATOR = "&&" | "||" ;
COMPARISON_OPERATOR = "<" | ">" | "<=" | ">=" | "==" | "!=" ;
What Expressions Currently Support
What Expressions Do Not Currently Support

Keying Strategy

Ultimately, it is up to you and your team how best to name your localization keys. Lokalized does not impose key naming constraints.

There are two common approaches - natural language and contextual. Some benefits and drawbacks of each are listed below to help you make the best decision for your situation.

Natural Language Keys

For example: "I read {{bookCount}} books."

Pros
Cons

Contextual Keys

For example: "SCREEN-PROFILE-BOOKS_READ"

Pros
Cons

Or - Mix Both!

It’s possible to cherrypick and create a hybrid solution. For example, you might use natural language keys in most cases but switch to contextual for legalese and other special cases.

java.util.logging

Lokalized uses java.util.logging internally. The usual way to hook into this is with SLF4J, which can funnel all the different logging mechanisms in your app through a single one, normally Logback. Your Maven configuration might look like this:

<dependency>
  <groupId>ch.qos.logback</groupId>
  <artifactId>logback-classic</artifactId>
  <version>1.1.9</version>
</dependency>
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>jul-to-slf4j</artifactId>
  <version>1.7.22</version>
</dependency>

You might have code like this which runs at startup:

// Bridge all java.util.logging to SLF4J 
java.util.logging.Logger rootLogger = java.util.logging.LogManager.getLogManager().getLogger("");
for (Handler handler : rootLogger.getHandlers())
  rootLogger.removeHandler(handler);
 
SLF4JBridgeHandler.install();

Don’t forget to uninstall the bridge at shutdown time:

// Sometime later 
SLF4JBridgeHandler.uninstall();

Note: SLF4JBridgeHandler can impact performance. You can mitigate that with Logback’s LevelChangePropagator configuration option as described here.