The grammar applies whether the name is Russian or not with some edge-case exceptions that can roughly be described as 'when it sounds weird and/or like somethi

The grammar applies whether the name is Russian or not with some edge-case exceptions that can roughly be described as 'when it sounds weird and/or like something else' i.e. they tend to be almost 'phonetic'. A name ending in -berg or the like, though, is a perfectly regular (for Russian) name that could just as easily be a Russian last name. An example off the top of my head: https://en.wikipedia.org/wiki/Ilya_Ehrenburg https://en.wikipedia.org/wiki/Ilya_Ehrenburg