An i18n engine with translation rules?

This is a long shot, but hopefully someone can help!

Some time ago I found an i18n engine that allowed you to define custom rules to improve the translation quality. Most i18n engines simply interpolate the argument to the translated string. This causes non-natural translations. An example is languages that use articles and apostrophes, like Catalan, French or Italian, or languages with cases, like German or Lithuanian.

This i18n engine let you define custom rules on how to generate those apostrophes depending on the argument that you're sending to the translated string.

Anyone knows something about it?

Thanks!