language: set JAMI_LANG variable

GitLab: jami-daemon#747

Change-Id: I4c87490fb21eb5e7c5f11deadf871f56755eb2f1

src/app/mainapplication.cpp

@@ -136,6 +136,7 @@ MainApplication::init()
     setWindowIcon(QIcon(":/images/jami.ico"));
 
     Utils::removeOldVersions();
+    qputenv("JAMI_LANG", settingsManager_->getValue(Settings::Key::LANG).toByteArray());
     settingsManager_->loadTranslations();
     setApplicationFont();