Impacted versions:
Master branch, should by 12.0

Steps to reproduce:
Install a third party addon with localization po file in i18n folder, even loading translation manually, the translation won't work, The console reports error: Translation .... not found in reference pot, skipping.
Reverse the change of  "odoo/tools/translate.py" in this commit, the issue was gone.

Expected behavior:
The po translation works as before.



odoo/tools/translate.py
'el_GR': 'Greek_Greece',
    'gu': 'Gujarati_India',
    'he_IL': 'Hebrew_Israel',
    'hi_IN': 'Hindi',
    'hu': 'Hungarian_Hungary',
    'is_IS': 'Icelandic_Iceland',
    'id_ID': 'Indonesian_Indonesia',
    'it_IT': 'Italian_Italy',
    'ja_JP': 'Japanese_Japan',
    'kn_IN': 'Kannada',
    'km_KH': 'Khmer',
    'ko_KR': 'Korean_Korea',
    'lo_LA': 'Lao_Laos',
    'lt_LT': 'Lithuanian_Lithuania',
    'lat': 'Latvian_Latvia',
    'ml_IN': 'Malayalam_India',
    'mi_NZ': 'Maori',
    'mn': 'Cyrillic_Mongolian',
    'no_NO': 'Norwegian_Norway',
    'nn_NO': 'Norwegian-Nynorsk_Norway',
    'pl': 'Polish_Poland',
    'pt_PT': 'Portuguese_Portugal',
    'pt_BR': 'Portuguese_Brazil',
    'ro_RO': 'Romanian_Romania',
    'ru_RU': 'Russian_Russia',
    'sr_CS': 'Serbian (Cyrillic)_Serbia and Montenegro',
    'sk_SK': 'Slovak_Slovakia',
    'sl_SI': 'Slovenian_Slovenia',