Web scraper for Football (Soccer) data with BeautifulSoup and Requests
Major Issues

Here are some major things that require attention:


indentation (PEP8 reference). Use 4 spaces for indentation
avoid using global variables. (Why are global variables evil?). If you need to share variables between functions of your program, you can pass them as arguments, or define these functions as method of a "scraper" class which would share instance variables
variable naming. The code is much more often read than written - by choosing descriptive variable names, you are improving the readability of your program. Variables like s, ext, t, z, l, l1 etc were bad choices


Next things to address


remove redundant parenthesis. For example, if (ext[0] == "/"): can become if ext[0] == "/":
address other PEP8 code style violations, in particular:


grouping imports
the use of whitespaces around operators in expressions
blank lines between top-level functions

use if __name__ == '__main__': for the main execution block of the program
since base_url and ligen are constants, name them properly


Web-scraping improvements


since you are sending requests to the same domain multiple times, you can improve on the performance by using session.get() instead of a requests.get() where session is initialized as session = requests.Session() once and re-used (reference)
you can use SoupStrainer to let BeautifulSoup HTML-parse only the relevant part of the page
think of using CSS selectors instead of find() and find_all(). For instance, soup.find("select", attrs={"name": "saison"}) can become soup.select_one("select[name=saison]"). It is not necessarily a better way to locate elements but it is quite handy to have it in your toolbox
have you tried to use pandas.read_html() to parse the table HTML block in the get_games() function? It might work to get the table in a dataframe(s) directly


Some simplified code constructs


here is a more concise and readable way to define seasons in the get_seasons() function using a list comprehension:

seasons = [
    [season.get_text(), season.get("value")]
    for season in soup.select("select[name=saison] option")
]





Overall, though, I think it would be a good idea for this code to go through several rounds of code reviews. 

Also, consider using a linting tool like flake8 or pylint, or/and a modern smart IDE like PyCharm - would help to catch a ot of stylistic and other mistakes.