feat(l10n): Allow to force language with a query parameter

This will be used by support application to always generate the support
 report in english. It may also be used to debug a language, or to
 temporarily show a page in an other language to take a screenshot or to
 share your screen with someone speaking another language.

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

lib/private/L10N/Factory.php

@@ -98,7 +98,7 @@ class Factory implements IFactory {
 				$lang = str_replace(['\0', '/', '\\', '..'], '', $lang);
 			}
 
-			$forceLang = $this->config->getSystemValue('force_language', false);
+			$forceLang = $this->request->getParam('forceLanguage') ?? $this->config->getSystemValue('force_language', false);
 			if (is_string($forceLang)) {
 				$lang = $forceLang;
 			}