Biełarusian

[Хворост]

I think, English ʃ is not velarized, and Russian has velarized ʃˠ and palatalized ʃʲ.

[Virginis]

Russian <ш> and Polish <sz> are written in IPA as [ʂ]. English <sh> is IPA [ʃ].

"Саn be", but is not. This type of pronunciation is thoroghly obsolete throughout all regions of Poland

It is archaic but still can be heard in eastern Poland and among Polish minorities in Lithuania and Belarus.

zi = ź = жь

No, Polish <ź> is just a palatalized <z> - IPA [ʑ]

[Vertaler]

Russian <ш> and Polish <sz> are written in IPA as [ʂ]. English <sh> is IPA [ʃ].

No English wiki, please. If you dig a little bit more, you will find their honest confession of using ʂ instead of ʃˠ - although ʂ has a different meaning. A Spanish friend of mine had been trying to pronounce Russian ш with his tongue pulled upwards, just as it was given in books describing the pronunciation of real [ʂ] - and he was incredibly surprised no Russian was speaking like him.

[Rōmānus]

and Russian has velarized ʃˠ and palatalized ʃʲ.

I am not sure ʃˠ even exists.

[RawonaM]

Both Russian and Polish <sz> are indeed velarized or retroflex for most speakers. There are some variations.

[iopq]

Actually Russian ш is a NON-DOMED post-alveolar and is slightly velarized. English sh is a DOMED post-alveolar. This means that the tongue curves making a dome-like shape.