Show warning dialog if NewGRFs use too many string IDs.

Show when reloading/changing NewGRF config, or starting new game.

src/lang/english.txt

@@ -3319,6 +3319,9 @@ STR_NEWGRF_BUGGY_ARTICULATED_CARGO                              :{WHITE}Cargo/re
 STR_NEWGRF_BUGGY_ENDLESS_PRODUCTION_CALLBACK                    :{WHITE}'{1:STRING}' caused an endless loop in the production callback
 STR_NEWGRF_BUGGY_UNKNOWN_CALLBACK_RESULT                        :{WHITE}Callback {1:HEX} returned unknown/invalid result {2:HEX}
 
+STR_NEWGRF_TOO_MANY_STRINGS                                     :{WHITE}Not enough string IDs available for all NewGRFs.
+STR_NEWGRF_TOO_MANY_STRINGS_DETAIL                              :{WHITE}Some names and text fields may be displayed incorrectly. Try using fewer NewGRFs.
+
 # 'User removed essential NewGRFs'-placeholders for stuff without specs
 STR_NEWGRF_INVALID_CARGO                                        :<invalid cargo>
 STR_NEWGRF_INVALID_CARGO_ABBREV                                 :??