Sorry you're finding this, OP. Speaking for myself, I like to meet mums from other countries. I find it interesting to learn about other cultures.
I must admit that I have been guilty of shying away from foreign mums who don't speak much English - not because I don't think I'd find common ground with them or wouldn't like them, but just because it was quite difficult to understand what they were saying, and it was awkward to constantly ask them to repeat themselves, or worse still pretend to have understood (to avoid asking them to repeat yet again), only for it to become clear further into the conversation that I had completely the wrong end of the stick. That's not a criticism of those mums ( I'm sure if I were to try to speak their language, I'd be pretty unintelligible too), but when you're spending the day with a toddler who struggles to communicate, you want your precious adult conversation to be easy.
But your English is perfect, so this clearly isn't the issue with you. You haven't mentioned your ethnicity OP (and of course, it shouldn't be relevant) but there seems to be a lot of division and mistrust around at the moment, unfortunately, particularly between different races. I know I'll get flamed now, but I think a lot of white English people are afraid to say or do the wrong thing (commit a micro aggression, mispronounce a foreign name more than once, use terminology that is now consided to be offensive). You don't say where you live, but I think this is particularly the case in areas where there aren't many people of different ethnicities...people just get the chilling effect from extreme positions seen on social media, without the balance of normal, everyday interactions that you get in areas with more mixed populations. This feeds into a sort of positive feedback loop, as illustrated by TigerLil's comments above...English people become wary of non-English people, so the non-English people feel the English are xenophobic, so they avoid the English people, so the English people become wary of the non-English people...and the more divided we become. I think it's very sad.
Of course, some English people are just xenophobic and therefore have no interest in being friends with you. But I don't think this is the case for the majority. I suspect that most are just a bit wary, and possibly a bit lazy about things like the small amount of extra work in explaining cultural references that you may not be familiar with, etc.
So what can be done? Maybe meeting other people in person, right from the off. Could you do some voluntary work at your local toddler group (or other activity that you can do with your child)? The other volunteers (generally a friendly and sociable sub-group) would be working with you, and get to know you that way, and perhaps friendship would develop. I hope you make some friends soon!