Yes, these are exceptions, I know. I was more getting at the fact that the English word ends in -ia, why doesn’t the Russian word end in -ия? Where does the English -ia ending come from in Siberia? I thought it came from Russian, but, apparently, it couldn’t have done, since the Russian word does not end in -ия.
I was curious about Добро пожаловать, so I looked the individual definitions. Добро is simply a noun meaning "good" (as in "good and evil"). пожаловать has several obsolete or dated meanings, but essentially means "to regard with favor, to like". So, it's seems sort of like "good to see (you)". The dated meanings are "to bestow, to reward" and "to visit, to come to see" - so it's more than just being glad to see someone, but also sending that gladness towards the person who has come to see you. Maybe.... I didn't have time to do an etymological search.
I tried to find declensions for the feminine noun сивирячка (Siberian woman), but Wiktionary was blank. I guessed at it, and came up with the following:
I'd appreciate any corrections from native-speakers. If it's correct, I'll try to add it to Wiktionary
In the US, we were told for many years that Siberia is where both the Tsar and the Soviet leaders maintained their prison camps, for criminals and political prisoners - that it is a bitterly cold place where people are exiled, there to die or return home broken in body and spirit.
I know Siberia can be very, very cold, and is covered in wilderness, but recently, I've seen some videos of young people in Siberia having a great time. It looked more like a Swedish resort, except everyone is speaking Russian.
The phrase seems very idiomatic, for one - probably developed over centuries.
Also: добро is a noun and хорошо is an adverb.
Since пожаловать is a infinitive meaning "to regard with favor, to like", it would sure seem like the adverb would be appropriate, but since the phrase uses a noun, it must mean something like "It is good to see (you)" rather than "good/nice/well seeing". It may be a question of degree - добро means actual goodness, in the sense of good and evil, so it's a bit stronger (I think) than хорошо.