>There would need to be significant concepts that people talking different languages think differently.
Not necessarily. If you study linguistics you will find that (human) languages are very similar. So it is possible, that lanugage is a central part of thinking, but the differences between languages are too minor to have significant effects.
That is a valid point. But to give context, the discussion I refer to was about whether there are reasons to keep small languages alive. And my opponents argument was that losing a languagle loses also ways to think, whereas my argument was that language is to a very good approximation means to communicate, nothing more, nothing less. so there is no reason to keep small languages alive. (My native language is a relatively small language)
Not necessarily. If you study linguistics you will find that (human) languages are very similar. So it is possible, that lanugage is a central part of thinking, but the differences between languages are too minor to have significant effects.
I agree with point 2 though.