I sometimes say "they're" or "their" in place of he/she. I don't think that's grammatically correct, though.

I just say "them". It seems right to me so I always keep on using it.

Use the singular 'they' for an indeterminate gender.

it

'They' would be confusing to me though since it indicates two or more people.

Never call a human being 'it'.

Straight from the English teacher's mouth.

?

French uses il for he/it and ils for they(m/m&f). I haven't heard about a singular they in French.

No.

English books and such would tell you to use "he" if you don't know the gender, but most scholars accept "they" now too.

Languages are sexist due to their age. In the US, using 'he' as a default was generally accepted until gender equality became known in the mid 20th century.

I can see how singular 'they' could be confusing if English isn't your first language, but if it is, then you've probably grown up hearing singular 'they' all the time.

I remember a while ago, I caught myself using they in the singular, and wasn't sure if it was correct, so I googled it and read the entire Wikipedia article.

'e was proposed for a while, since it could be a shortened version of 'he' or 'she.' Thank God that did not catch on

And to the person that said singular they could be confusing, you can state it first with a 's/he' and then switch to 'they/their' for the rest of the sentence. That shows an unknown gender.