The word تساهل in persian means to take easy, from سهل in Arabic but the Arabic dictionary says "indulgence". I don't understand, could you explain please.
Yes that's because you google it. If you read further though in this link http://webcache.googleusercontent.com/search?q=cache:BHrudhlkh60J:www.almaany.co
You'll find there are different meanings to the word. It depends if it is verb or noun too.So confusion is easy to happen.
But the word does derive from سهل which means easy ( you are right).
Now if it is Tasahol it is a noun , while if it is Tasahal it is a verb.
The thing is Arabic is a very rich language one word can mean a lot of things depending on context and grammar. Also you have so many words for expressing one thing on different levels.
For example Love has over 35 synonyms! See here if you're interested http://webcache.googleusercontent.com/search?q=cache:AmNiC9hvk0UJ:www.naabd.com/
For future reference use this website it is very good and quiet reliable http://www.wordreference.com/aren/%D8%AA%D8%B3%D8%A7%D9%87%D9%84
. You can also use google translate if the word is very simple.
As for Farsi I am not sure what it means, but my boyfriend speaks Farsi and he doesn't think it holds the exact same meaning as it does in Arabic.
Hope this helps.