What are you suggesting they show first? Most people would argue that Google's translation service is the best of the free/ad-supported options out there.

Even Bing shows Google's translator first (after their own inline version).

At the beginning there were other, better options but Google Translate was still on top... Like IE on Windows: other were better, but IE was preinstalled...

But you are on Google's site, it's a company, not a public service.

There are different rules when you use a dominant position in one market to gain share in another.

This is equivalent to the Microsoft/IE thing.

https://en.wikipedia.org/wiki/Competition_law

They're not challenging Google's dominance of search or projecting responsibilities on them as a service due to that monopoly.

They're simply objecting to Google using its dominance in search to gain dominance in, for instance, digital translation.

https://en.wikipedia.org/wiki/United_States_v._Microsoft_Cor....

There are laws about what companies can do. And using a dominant market position in one market to help them in other markets can be an anti-trust violation (see Microsoft and the browser wars).