Wow, that's a LOT of languages!
I grew up in the Midlands in England, so I guess it's a similar situation to you with Igbo, in that I can understand most of the British and Irish dialects. Southerners and northerners struggle to understand one another, though. It also means that my accent is neutral enough that I can be understood by most English speakers. When I came to Australia and was helping out at my daughter's school, the teacher would get me to do some reading tests and would always give me the Scottish girl to test. I'm pretty sure it was because she struggled to understand her accent. 😆 I recall the poor girl getting rather stressed when an assistant was listening to her reading and kept correcting her, when she was saying the right word, but it didn't sound like it to an Australian's ear.
Hahaha... Exactly. I've been enjoying the scouse accent so much. Both scouse and Irish accent usually cracks my ribs whenever I listen to it. As for the main English (most part of England), it's more Shakespearean and always sounds so poetic.
Yet, people will just say 'English Language' without realizing that some native English speakers finds it hard to understand themselves whenever these accents comes into play. Haha.
This shows how diverse these languages can be.