This might help if you are trying to use multiple custom dictionaries especially if you don't have sudo access to the system aspell dictionary directory ...
I created three custom dictionaries (or are they word lists) using "aspell create master" and found a way to use them ...
1) Create 3 word lists, one word per line, wordlistA.txt, wordlistB.txt, and wordlistC.txt.
2) Create 3 masters ... aspell --lang=en create master ./my_LANG-dictA.rws < wordlistA.txt - repeat for B and C (lang needs to be already installed, I think any lang will work).
3) Create 3 multi files, my_LANGA.multi, contents: add my_LANG-dictA.rws) - repeat for B and C. Where my_LANGA can be any name in the same case as explained in the aspell manual.
4) Use any one of them (A B or C) with pspell ...
<?php
$pspell_config = pspell_config_create('my_LANGC', '', ''. 'utf-8');
pspell_config_dict_dir($pspell_config, <location of my_LANGC.multi>);
if (($pspell = pspell_new_config($pspell_config)) == false) {
    echo 'pspell_new_config() for LANGC FAILED!');
} else {
    $word = 'PHPisgreat'];
    if (pspell_check($pspell, $word)) {
        echo "$word: Valid spelling";
    } else {
        $suggestions = pspell_suggest($pspell, $word);
        echo "$word: suggestions: $suggestions"
    }
}
?>

The language arg for pspell_config_create() is the basename of the .multi file.
Note that I do not have a file $HOME/.aspell.conf.
Note that my .multi and .rws files are in the same directory, which I think is necessary.
The wordlist files are not needed once the masters are created.