As I mentioned before, some mods support more than one language. The language tags aren't mutually exclusive. For example, SkyUI is tagged with English, French, German, Italian, Japanese, Polish, Russian, and Turkish. If you block /any/ of those language tags, you're blocking SkyUI, and that's just one example of many. And, no, approaching it from the other end - only listing mods that are tagged with English - won't work either, because a lot of English-only mods don't even bother tagging themselves with English. So you're still blocking a lot of mods you didn't intend. Tag filtering isn't flexible enough for this task.
