Internationalize Your Way to Cleaner Code

If your project is localized, it’s probably internationalized. If it isn’t, there’s a good chance it’s not.

Depending on your familiarity with those terms, the above may seem annoyingly opaque or blindingly obvious. If it’s opaque, I promise to clarify. If it seems obvious—that this is how things are and how they should be—I’d like to make a case for internationalizing regardless of whether you plan to localize.

Even if it never ends up helping someone who speaks another language, internationalization is worth it because the process concretizes some of the fundamental principles of clean code.

So many letters

Localization and internationalization are a lengthy couple of words, so I’m going to use the abbreviations L10n and I18n often (and regardless of whether it’s at all grammatical to do so).

They’re also commonly conflated, so let me take a moment to brighten a line.


L10n means taking an application made for one group of people and adapting it for another.

Usually the second group speaks a different language than the first, but language translation isn’t the only change made during L10n. It may also be necessary to alter the way numbers are separated (1,234,567.89 might become the internationally more common 1 234 567,89), or to reformat dates.


I18n refers to the process of shaping code to make L10n less painful.

At its core, it involves gathering up all the things that might change when localizing (for example, the name of the button a user clicks to abort some action) and extracting them to a single, easily editable place. That way, when the time comes for L10n, supporting a second locale is as easy as swapping in a new translation file.

I18n is typically thought of as the thing you do to prepare for L10n, but it isn’t strictly necessary to I18n before you L10n. All apps are technically localizable—it’s just that some can be localized a lot more easily than others.

To see why you should I18n before you L10n, consider the alternative. Localizing a totally non-I18n app means creating a copy of the codebase and hunting through it—file by file, function by function—to find and replace every localizable thing. Possible, but painstaking.

I18n-ing a file converter

Here’s a simple example of how you might go about internationalizing some existing code.

The class below contains the high-level steps for converting an audio file from one format to another. It has not been internationalized.

 1 class Converter
 2   def initialize(processor)
 3     @processor = processor
 4   end
 6   def convert(file)
 7     puts "Converting #{} to #{@processor.target_format}..."
 8     converted_file = @processor.execute(file)
10     puts "Conversion complete!"
11     return converted_file
12   end
13 end

I18n-ing this class comprises swapping out its string literals (“Conversion complete!”) for references that represent the message in the abstract (conversion_complete). Here’s one way of going about it:

 1 class Converter
 2   def initialize(processor, translator)
 3     @processor = processor
 4     @translator = translator
 5   end
 7   def convert(file)
 8     puts @translator.converting(, @processor.target_format)
 9     converted_file = @processor.execute(file)
11     puts @translator.conversion_complete
12     return converted_file
13   end
14 end

Now, instead of being bound to the strings that were soldered into it, the class will use the messages defined in the translator, whatever the language and however they are formatted. Localizing the code becomes as simple as creating a class that contains translations for a given locale and adheres to the translator interface:

1 class EnUS
2   def self.conversion_complete
3     "Conversion complete!"
4   end
6   def self.converting(filename, target_format)
7     "Converting #{filename} to #{target_format}..."
8   end
9 end
1 class EsMx
2   def self.conversion_complete
3     "¡Conversión completa!"
4   end
6   def self.converting(filename, target_format)
7     "Convirtiendo #{filename} a #{target_format}..."
8   end
9 end

The way I internationalized this code is a little unusual. In practice, it’s more common to put translations in language-agnostic data interchange files rather than defining them in code. Rails I18n, for example, uses YAML.

I did things unconventionally to keep things simple, and because my intent isn’t to discuss or advocate for a particular implementation of I18n, but to point out what I18n achieves in the abstract.

Good for code, not just users

I18n makes L10n easier. If the project you’re working on will be used by people outside the locale in which it was developed, you should internationalize it—ideally as early as possible.

But it’s worth internationalizing even if you know you’ll never localize. I18n embodies some of the most important qualities of good software design, and applying it will leave you with a codebase that is more pliable when it needs to change.

The ideas it represents are simple but significant: use abstraction, depend on abstractions, and have a single reason to change.

Use abstraction

To create an abstraction is to come up with an interface that exposes what the underlying thing can do in the abstract (e.g., store some data) while hiding the details of how it does that thing (by sending SQL statements to Postgres/in memory/with a robotic arm and chalk).

Consider the use of @processor above. @processor is an abstraction. All the messy details of how to convert an audio file from one format to another might have been embedded in Converter, but the use of abstraction means it doesn’t need to concern itself with them. Instead, all it needs to know is that a processor is something with an execute method that takes a file and returns a file.

Internationalizing Converter was in part the process of replacing detail with abstraction. The original version concerned itself with the details of the progress messages, whereas the I18n Converter is blissfully ignorant of them. Its translator’s converting method could return Mandarin, Spanish, English, or Konkani, and it would be equally happy with each. It doesn’t need to know whether its translator has the strings hardcoded into it or reads them from a file, or any other details of its inner workings.

Depend on abstractions

One of the big ways to benefit from using abstraction is to depend on it instead of concretion. Doing so affords a system with greater flexibility, and makes it more resilient to change.

Even though Converter uses the abstraction puts rather than taking on the details of how exactly to get a string printed to the console, it fails to depend on that abstraction. Instead, it has a concrete dependency on Kernel, via its direct use of puts to output messages to the user. (While it looks like puts is being called on nothing, it’s actually a method on Kernel, and available pretty much everywhere because Kernel is included in Object.)

The result is a class that is less amenable to a certain kind of change. If we wanted to adapt Converter for a context other than the console, we’d need to make changes in multiple places (all the puts statements) instead of just one (the abstract I/O dependency we might have passed on instantiation instead).

Admittedly, this change wouldn’t be painful at all if simple little Converter comprised the whole system. But code is cheap, and systems grow. Much harder to make a change like this when you have to touch a dozen long files to do it. Breaking something becomes likelier, and enjoyment levels range from monotonous to excruciating.

We could have rewritten Converter to abstract away the message details to EnUS, and then depended directly on that class:

def convert(file)
  puts EnUS.converting(, @processor.target_format)
  # ...

  puts EnUS.conversion_complete
  # ...

But by relying only on the translator abstraction passed on instantiation, Converter can be passed and work happily with EnUS, EsMx, and anything else that implements the translator interface.

Single responsibility

I18n moves a system towards the ideal of one responsibility per capsule (function, class, etc).

The original Converter concerned itself with not only the high-level steps involved in converting an audio file (in this case, passing the file to some processor, returning the result, and informing the user of the progress), but also the lower-level details of what exactly to say to the user at a given juncture. By extracting those details into a translator class, the class has a simpler and more obvious role.

In addition to the increased clarity this affords, limiting each capsule to a single responsibility makes the system as a whole easier to change. When a reason to change, such as message localization, is shared by many parts of a system, they all have to change in order for the concern to be changed. Any time you change the inner workings of a capsule, you chance breaking it or another capsule that depends on it.

But by limiting how many details any given capsule knows, both internally and about its surrounding context, you can lessen a system’s vulnerability to change.


I18n is good for users because it makes L10n easier, which means more software that is more accessible to more people.

I18n is good for code because it fosters abstraction, dependence on abstraction instead of concretion, and limiting how much each capsule knows. These things lead to software that is better able to adapt to changing requirements.

What’s not to like?

Ben Spatafora, Software Craftsman

Ben Spatafora is a former 8th Light employee.

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