Please find my response below.
Find a car: to fix it you need to change input tag to button, since input tag values are not being translated to not break your application after submit.
Leave us a message: It is being generated by Zopim, you may talk to them and ask if it will be possible for them to use their form in a different language if you pass them the language code. I'm not sure that they will support all languages, also if you are going to provide support in English and Russian only it won't be good, because you will end up getting support requests in different languages which your support team doesn't speak.
If you want to edit the contact us placeholders, you need to create a temporary page, write the texts inside of the placeholders on that page in <p> tags, edit them and they will be updated on all pages. Then you can remove the temporary page.
I'm not sure about the Custom Us, I don't know where to look. In general if you can see it's content in HTML then it can be translated.