[FIX] http_routing: mitigate key does not exist in context for lang

closes odoo/odoo#83880

Signed-off-by: Olivier Dony <odo@odoo.com>

addons/http_routing/models/ir_http.py

@@ -402,7 +402,7 @@ class IrHttp(models.AbstractModel):
             if nearest_lang:
                 lang = Lang._lang_get(nearest_lang)
             else:
-                nearest_ctx_lg = not is_a_bot and cls.get_nearest_lang(request.env.context['lang'])
+                nearest_ctx_lg = not is_a_bot and cls.get_nearest_lang(request.env.context.get('lang'))
                 nearest_ctx_lg = nearest_ctx_lg in lang_codes and nearest_ctx_lg
                 preferred_lang = Lang._lang_get(cook_lang or nearest_ctx_lg)
                 lang = preferred_lang or cls._get_default_lang()