Translation:Polish is more similar to Russian than to English.
In the version that reads "Polish is more like Russian than English," there's a subtle ambiguity, since that sentence could be interpreted as "Polish is more like Russian than like English" (which is the meaning of the Russian sentence), or it could be interpreted to mean, "Polish is more like Russian than English is like Russian."
First, the most natural phrasing of your example: "Polish looks more like Russian than English"
You can use "looks like" figuratively:
- It looks like rain. (From the appearance of the sky, I think it will rain.)
- It looks like he's guilty. (from the evidence)
- It looks like I'll have to go to Russia. (circumstances indicate)
But if you use it in this example, it would make people think you're referring to the appearance of written Polish, e.g. the alphabet - and that's probably not true. Just as if you said "sounds more like" you'd be referring to the sound, which I think might be true.
The most natural translation in this exercise would be "Polish is more like Russian than English." But I think they've made the right choice for suggested translation; theirs is OK, and more clearly related to the Russian.