Design and implementation of translation system for desktop software

A web-based, crowd-sourced translation system.

I just finished building AppTranslator, which is a third iteration of a system that allows people to contribute translations for SumatraPDF.

This post describes the big picture of how it’s designed and implemented. Everything I discuss is open-source, so you can dig into code for more details.

The goals of translation system were to make it easy for me to add new strings for translations and easy for other people to contribute translations.

I call it a "system" because it consists of several parts that are designed to act as a sensible whole.

How translations are stored in C++ code

I try to design for simplicity of implementation to minimize the amount of code to write. Often it means that I reject popular solutions if I can design a simpler one.

SumatraPDF is a C++ desktop software for Windows. There already is a popular system for maintaining translation for such programs: use resource dlls, one dll per supported language. The translations are kept in .rc files as strings and referred to by numeric ids from code via LoadString() API.

That would be very clumsy both for me (when adding new translations) and for potential translators (they have to edit files in a cryptic format). It also requires distributing multiple dlls (I prefer to ship my apps as single executables).

Managing translation strings in C++ code

The first part of the system was therefore a new design for managing translation strings in the app.

All translations are marked with _TR() macro in the code.

A python script extracts those strings from the source. It then reads translations provided by contributors and generates a C++ file with strings. _TR() macro evaluates to calling a simple supporting code in Translations.cpp that looks up a translation of a string given currently selected language.

How translations are contributed by users

SumatraPDF is an open-source project so I rely on contributions from users to keep it translated.

The system for collecting contributions had 3 iterations.

In first iteration, I had a single text file with all translations.

It looked like this:

String to translate
de:German translation
fr:French translation

Another string to translate
de:another German translation

People would download the latest version of the file from svn, add missing translations and e-mail it to me. I would check-in that to svn and re-run the script that rebuilds C++ file with strings.

At some point the file became very big so I split it into multiple files, one per language.

It was working ok but the process of submitting translation was time consuming for translators and the process of updating the code was time consuming for me.

For that reason I built a web-based service which makes it much easier to contribute a translation.

I also added the necessary API endpoints in the server to allow writing scripts for automating uploading strings to translate and downloading latest translations.

The design of web-based UI

A web-based UI for editing translation is not a novel idea. However, my brief research shows that few do it well.

I try to be pragmatic about things. If a decent 3rd party system with enough flexibility to meet my needs already did exist, I would rather use it than develop my own (writing code takes time).

I’m tempted to say that I designed for simplicity but, while being true, it’s also rather vague. More accurately: I designed for simplicity of the translator workflow.

You can judge the UI yourself but let me point out few specific points:

  • it takes 2 clicks from main page to a point where you can submit translation. The first click is to select the project (as AppTranslator is designed to support multiple projects) and the second click to select the language
  • on the page for a given language, the untranslated strings are at the top. The rest is sorted
  • I don’t require creating an account for AppTranslator but authenticate with Twitter

Those might seem like obvious points but I found that other systems I’ve surveyed were baroque enough to inspire Kafka.

Ubuntu’s translation system gets a special recognition for amount of bureaucracy, complicated workflows (joining a translation team to submit a translation?) and bad copy (they feel it’s important to inform you that in order to contribute a translation you need an internet connection, among many other useless bits of information).

Mozilla is marginally better

Technical specs

AppTranslator is written in Go and open-source (BSD license).

I run it on Ubuntu server. It’s possible, but not easy to run your own instance.

SumatraPDF is also open-source. The code is in C++ with a bunch of python helper scripts to automate interaction with AppTranslator server.