Resolve catcode regime conflict

revealed in LyX testing

tex/polyglossia.sty

@@ -2021,10 +2021,13 @@
     % Since captions might float to other language regions,
     % we need to specify the language here (#542)
     \cs_set_eq:cc { __xpg_save_caption:n } { @caption }
+    \cs_new:Npn \xpg@current@opts {}
 
     \cs_set:Npn \@caption #1 [#2] #3
       {
-            \__xpg_save_caption:n { #1 } [ { \selectlanguage*[\xpg__current_options_tl]{\languagename}#2} ] { #3 }
+            % we might be outside of l3 catcode regime
+            \tl_set_eq:NN \xpg@current@opts \xpg__current_options_tl
+            \__xpg_save_caption:n { #1 } [ { \selectlanguage*[\xpg@current@opts]{\languagename}#2 } ] { #3 }
       }
   }