I'm worried about influencing outcomes in the EU due to language barriers, especially on boring and "unsexy" issues like Internet regulation. It'd be important for the EU to be able to vote for representatives regardless of your primary jurisdiction. Even if I manage to convince most of the representatives from my region, they will be outvoted by the French who had a big hand in passing the proposal forward the last…
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).