It's certainly a cat-and-mouse-game until you've added the obvious idioms, but that only lasts a few iterations, because the users will quickly have to come up with new ones that get less useful as their understanding gets less wide-spread. It's one of those situations where you can absolutely win by and large, even if you don't catch everything. If you catch 95-99%, you're done.

Bangladesh has a population of 160m, and almost all speak Bengali, which is also used in India by a significant minority. It's not like we're talking about ignoring Liechtenstein. It won't eat up the profits by having someone add 10 rules to a filter list for a target audience of 200m+, even if they are poor.