I find that unlikely to believe. Yes, the de-facto working languages in Bruxelles are English and French, but chances are everyone knows both (or even English better). If you send material to MEPs of any country, they will be able to read it if they want - there are dedicated translation services, as you might imagine in an org working with dozens of different ethnicities.

Language acts simply as a constituency signal (“not in my language? Not a voter of mine...”). That is expected and even legitimate - why should a MEP listen to other voices over the ones of people they actually represent? If you really want to influence a MEP, you would get better chances by finding allies in his constituency. This is not really different than with national parliaments.

In terms of this or that national block outvoting a position, it is less frequent than one would expect, and depends largely on how European parties organise. Most parties have some sort of nominated board that agrees a line for the entire group, regardless of national boundaries. Some countries might have a larger influence on the group because of their electoral dynamics (German MEPs for the Greens, for example, will outnumber Italian ones to ridiculous degrees; and some parties are single-country, typically the isolationist ones), but that’s usually not the case in major parties (PSE and PPE).