There are over 6.000 languages according to Wikipedia.
Over 50 languages are spoken from over 80% of the people as their first language.
So, where to start?
If you live in the EU like me, it is easier to start with an languages which has its within this region. Why?
The roots are basically the same.
They are called the indogermanic languages (3 billion people).
Within these languages there are the germanic languages (500 Mio people).
So, for me it is easier to start with a new germanic languages like English or Danish.
If I start with French I get access to the roman languages (although part of the indogermanic languages) like Spanish or Italian which are spoken from over 700 Mio people.
A different kind of languages for me are Mandarin, Japanese or Arabic.
In English, French or German you talk, write and read the same letters.
In Japanese for example there are three different kinds of alphabets - Hiragana, Katagana and Kanji.
To learn these languages is like starting from scratch.
There is no shortcut.
But if you master them a whole new world is opened to you (like Mandarin 1,3 billion people).