[FIX] add missing language names to the language switcher

Even though the Thai documentation has been built and is available, it
didn't show up in the language switcher. This is because it needs to be
given a "language name" first.

This commis add the language names corresponding to the newly added
translations (namely, into Thai and Japanese).

closes odoo/documentation#10735

Signed-off-by: Tiffany Chang (tic) <tic@odoo.com>

conf.py

@@ -252,11 +252,13 @@ languages_names = {
     'es': 'ES',
     'fr': 'FR',
     'it': 'IT',
+    'ja': 'JA',
     'ko': 'KO',
     'nl': 'NL',
     'pt_BR': 'PT',
     'ro': 'RO',
     'sv': 'SV',
+    'th': 'TH',
     'uk': 'UA',
     'zh_CN': 'ZH (CN)',
     'zh_TW': 'ZH (TW)'