Hey Isabel. I would definitely create your blog in your native language if that is the one that you write better in. If your English grammar isn’t impeccable, you will have a hard time getting a loyal audience of English speakers. A blog written in English has the potential for a larger audience, but a blog in your native language will have less competition and the potential for a far more LOYAL audience. I hope that helps!
Working with advertising networks isn’t your only option when it comes to selling ads. If you end up with enough traffic, advertisers may come directly to you and ask you to place their ad on your site. You can also contact advertisers yourself. The biggest difference from the above mentioned option is that there is no middle man, which means you can set your own ad rates.