You can improve the spell checker without touching the dictionary. For single words (no spaces), you can add your words to one of these files:

• spelling.txt: words that the spell checker will ignore and use to generate corrections if someone types a similar word
• ignore.txt: words that the spell checker will ignore but not use to generate corrections
• prohibited.txt: words that should be considered incorrect even though the spell checker would accept them

These files exist for each language. Words in file of the all directory, will be added to each language.