I'm not quite sure I understand. The name of the scenario is decided entirely by the folder. The language file has no say over the scenario name as far as I know. The scenario's XML file must be named <folderName>.xml and the language files must be named <folderName>_<language>.lng.
For example, running megaglest --list-scenarios on the latest stable release produces (EDIT: except the benchmark scenario isn't part of the release):
Scenarios found:
===========================================
amazones
amazones_light
anarchy
beehive_castle
beginner_1
beginner_2
beginner_3
benchmark
capture_enemy_flag
duel
egypt_mayhem
indian_attack
kill_the_magic
magic_can_do_it
my_island
norsemen_attack
one_hope
siege_of_despair
storming
tech_and_magic
tough_duel
waterworld
===========================================
Total: 22
I can run, say, Egypt Mayhem with megaglest --load-scenario=egypt_mayhem, which works fine (despite the fact that in-game, the translator replaces underscores with spaces and Capitalizes The First Word Of Everything). The same works for scenarios with an actual language file, like storming.
If this wasn't a misunderstanding of the commands, can you please give a specific example of how the features are incompatible?