Hola,
1. English allows you to communicate with people from all over the world and currently there's only this forum and everyone uses English in it. (Although the website is offered in English, French and Spanish, so it maybe would made sense if each one of these languages had it's own forum... but then it would be a little less international experience... just saying)
2. If custom texts were used to calculate your typing speed average then anyone could create trivial texts to improve their ranking (for example texts that used only one letter)