[FIX] tools: export UTF-8 characters

- Install Babel 2.3.4 as specified in the `requirements.txt`
- In a Python file, do not add the line `# -*- coding: utf-8 -*-`
- Create a translatable string with a non-ASCII character, e.g.
`Amount in €`
- Export the translation

The exported term is incorrect: `Amount in â¬`.

Since the default encoding for Python 3 is UTF-8, it is logical for the
Babel extraction to use it as a default encoding.

The issue was solved in Babel 2.4.0 with commit:

https://github.com/python-babel/babel/commit/33a8fc40d417b401162e2d20021fcbebcc4ab7db

opw-1984480

closes odoo/odoo#33671

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

odoo/tools/translate.py

@@ -953,8 +953,11 @@ def trans_generate(lang, modules, cr):
         extra_comments = extra_comments or []
         if not module: return
         src_file = open(fabsolutepath, 'rb')
+        options = {}
+        if extract_method == 'python':
+            options['encoding'] = 'UTF-8'
         try:
-            for extracted in extract.extract(extract_method, src_file, keywords=extract_keywords):
+            for extracted in extract.extract(extract_method, src_file, keywords=extract_keywords, options=options):
                 # Babel 0.9.6 yields lineno, message, comments
                 # Babel 1.3 yields lineno, message, comments, context
                 lineno, message, comments = extracted[:3]