In order for Aspell to be able to correctly recognize a dictionary based on the setting of the LANG environment variable the dictionaries need to be located somewhere Aspell can find them and they need to be multi dictionaries. Where Aspell looks for dictionaries depends on the value of the dict-dir and word-list-path option.
dict-dir is generally prefix/lib/aspell, and word-list-path is generally empty.
Each dictionary that you expect Aspell to be able to find needs to have a name in the following format:
where language is the two letter language code, region is the two letter region code, variety is any extra information to distinguish the word list from other ones with the same language and spelling. Multiple varieties can be used by separating them with a '-'. Finally, size is the size of the dictionary. If no size is specified then the default size of 60 will be assumed.
en.multi en_US.multi en-medical.multi en-medical-85.multi en-85.multi de.multi