[FIX] im_livechat: fix translations for embed live chat

Before this commit, templates of the live chat embed were not
translated. Indeed, translations for the live chat module are
never loaded.

This commit fixes the issue by loading the live chat translations
at the same time templates are loaded.

opw-3509309

closes odoo#141819

Signed-off-by: Alexandre Kühn (aku) <[email protected]>

Author: tsm-odoo

addons/im_livechat/static/src/legacy/public_livechat.js

@@ -84,7 +84,13 @@ var LivechatButton = Widget.extend({
             }
             this._rule = result.rule;
         }
-        return this._loadQWebTemplate();
+        const proms = [this._loadQWebTemplate()];
+        // Translations are already loaded in Odoo frontend. Only load them if
+        // we are in an external page.
+        if (!session.is_frontend) {
+            proms.push(session.load_translations(["im_livechat"]));
+        }
+        return Promise.all(proms);
     },
     start: function () {
         this.$el.text(this.options.button_text);