Yes, language evolves. Currently, this is almost certainly grammatically incorrect, "they" being the third person plural and (not shown here, but assumed) the speaker being singular.
"They" is being pressed into service as the non-derogatory, gender-neutral third person singular that's missing in english. So "they" has started to mean both third person plural and unspecified third person singular. The previous solution was that "he" meant both "male" and "unspecified". So previously women got their own pronoun, men didn't, now we have a harder time telling whether there's a single person or a group.
Both solutions have their quirks, both work at some level.
"As long as they give a good talk" - you're not talking about one specific person but in fact a general population of speakers.
The pronoun refers to "speaker", singular, yet indefinite, we don't necessarily know who it is.
Let's substitute "they: "problems a speaker at a conference might have, as long as they give a good talk/presentation."
Yep, works for me, but I think the "they" definitely talks about about that single (if indefinite) speaker. Yet we use the plural of the verb ("give"), so the sentence is confused, grammatically. I wonder what will give as this evolves, whether "they gives" becomes acceptable or we simple leave "they" grammatically plural even when it is semantically singular.
Language. Fun times!
"They" has been grammatically correct for single person of unspecified gender for hundreds of years. Do a little research before saying ignorant things.
I also find it weird that German and Spanish inject gender into every noun, although I do get that there's little meaning behind it (from the little quizzing I've given speakers of each)