Some languages use more diacritics than others. This is relevant for Latin-based languages, like Vietnamese and Min Nan, where the diacritics are far more complicated than in languages like French. And it is also relevant for Indic and Southeast Asian languages, which have a lot of signs above and below the the line. Currently in core these languages ask for larger line-height (see skins/common/shared.css).
This is an important consideration. Maybe the line spacing should just be increased for all languages. And maybe only for some languages, but the code that does it should be cleaner and more robust than it is now.