[FIX] website_links: support foreign language for links graphs

When a user creates a link that is tracked, an interface with graphs is
presented to him so that he can track the performance of his tracked
link. Unfortunately, these graphs did not work when the site was in a
foreign language. This was due to the fact that the code had not been
designed to handle this. This commit fixes the code so that it works in
all languages.

Note that the data is received via RPC and the python code format the
dates for the current language of the website. So we had to do a little
hack to make it work properly.

Steps to reproduce the issue:
- Install website_links module
- Go to the website app
- Click on Promote > Link Tracker
- Create a tracked link
- Visit the link
- Install Arabic (Syria) for your website
- Check the stats of your link in Arabic

=> There is a traceback and the data is not displayed.

task-3289167

closes odoo/odoo#119375

Signed-off-by: Outagant Mehdi (mou) <mou@odoo.com>