AはBと同じくらい... comparative construction

Question

From this post I learned that I can change subject marker が with を (Aの方がB・・・） and it will be completely fine, but can I do so with 「AはBと同じくらいC」 construction?

For example, I need to say "He is as good at English, as at Russian". How should I deal with it?

1. あの人は英語がロシア語と同じくらい良く話します

What I wanted to say by this sentence is that "Regarding him, it is English that he speaks as well, as Russian.", but I'm afraid that cannot do so because, I belive, が denotes the subject that is doing the speaking.

But I believe that this sentence would be fine:

2. あの人は英語がロシア語と同じくらい上手です。

Also, I tried an option with で to indicate the means of speaking.

3. あの人は英語でもロシア語でも同じくらい良く話します。

Even if the 2nd one is perfectly fine, I'd like to know how to say the same thing by using the same pattern but with verb 話す

Answer 1

"He is as good at English, as at Russian".
あの人は英語がロシア語と同じくらい良く話します。

Your sentence is not correct, I'm afraid. You should instead say...

あの人は英語がロシア語と同じくらいよく話せます。

... using the potential form 話せる, "can speak".

You can use 「[Noun] + が + [potential form of a transitive verb]」 to mean "can do [object]". E.g. 「漢字が読めます」"can read kanji" 「コーヒーが飲めます」"can drink coffee"

To use 話します here, you use を, as in:

あの人は英語をロシア語と同じくらいよく話します。

(but this can also mean "He speaks as much English as (he does) Russian" or "He speaks English as often as (he does) Russian." To avoid the confusion, you could instead say 「あの人は英語をロシア語と同じくらい上手に話します。」)

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あの人は英語がロシア語と同じくらい上手です。

Sounds perfectly fine.

You use が with adjectives expressing one's emotion, feelings, or skills, such as 上手だ、得意だ、好きだ、欲しい、こわい、心配だ etc. E.g. 「英語が下手です」"poor at English" 「音楽が好きです」"like music" 「地震が怖いです」"be scared of earthquakes"

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あの人は英語でもロシア語でも同じくらい良く話します。

Sounds okay to me, but it could mean "He speaks a lot both in English and in Russian".

To more clearly say "He speaks both English and Russian (equally) well/fluently", I think you can say...

あの人は英語(で)もロシア語(で)も同じくらいよく話せます。
あの人は英語(で)もロシア語(で)も同じくらい上手に話せます。

...using potential 「話せる」. Of course you can also say:

あの人は英語もロシア語も同じくらい上手です。