[dundarious]

Diaeresis is used in English as well. The New Yorker writes “coordinate” as “coördinate”. It has the same meaning as in many European writing systems — “pronounce independently”. So it’s like “co ore” not like “core”.

It’s also common to see it in loan words and proper names, even with a different meaning.

[rippercushions]

In Russian ë is a completely separate letter pronounced "yo". This is non-intuitive to English speakers, which is why the name in question is almost always anglicized as Pyotr, not "Pëtr".

[dundarious]

> It's really weird seeing letter ё in English language title.

It’s not, for the varied reasons I gave. I know that this is yet another variant. I agree there is a problem with it in that its meaning is not well-known (so you may want to use more well-known alternatives), but not that the diacritic itself is “weird” or foreign to English language users.

[pessimizer]

It's weird because it doesn't make sense, not because it's a diacritic.