In some instances, a new species' name will not respect the lang file and instead display as pixelmon.<species>, which looks very buggy and can cause confusion in servers. (note that the name was correct in some instances, such as in the player's party display)
The instances of this issue I could find were:
In the battle gui:
- the display name next to the sprite
- in the battle text (this is the biggest issue since it can cause confusion in PvP battles)
- when the Pokémon learns a move
- when it is sent to the player's pc
There may be more instances that I didn't notice in my testing.