Asking another pax to put his/her seat forward *is* difficult. People are often hostile - when packed in so tightly next to strangers, people's need for some privacy seems to expand. Therefore, however politely expressed a request might be, normally even the act of looking in someone's direction and talking to them produces an aggressive reaction. Of couse there are honourable exceptions, thankfully many of them.
This is especially the case when the recline-perpetrator is female, (or the recline-perpetrator is a child and you are addressing yourself to its mother). A male stranger is perceived as a threat (if you don't smile) or cheesy (if you do).
Unless the recline-perpetrator has spoken, you don't know what language he or she speaks, if any. Perhaps they just grunt. If you don't have a language in common, it's going to be difficult to get your message across. The effort is likely to increase hostility, and when you summon the help of cabin crew (if they have any better language skills than you) the atmosphere is already heated.
So, let's not make this conditional on pax's linguistic skills, gender, size, and persuasiveness. Just lock the blóody seats upright. There's plenty of built-in recline in this position already.