I imagine a lot of it is segregating your content. All strings in one file, etc.

It'd be an interesting test to take our eight-language set of localization strings and compress them in UI order and language order and see if there's much of a difference. (UI order is all languages for one dialog element, then all eight for the next, etc. Language order is all the English first, then ...)

I'd definitely like to hear Kevingadd's tips though.