Latin. Most wetern languages come from latin. It would be easy to learn others when knowing latin
Discussion
Had that in school.
Not fun to learn, basically nobody uses it.
I've heard it is easier to learn other western languages when you know latin
Yes, that's correct. They employ pretty much the same rules and you can draw similarities between expression and words. Otherwise it's very boring.
You can also learn another latin-based language and get a similar effect. So for example if you learnt Spanish, you'd be able to understand a fair bit of Italian.