To spellcheck the code in Vim for English/German/Finnish

From the vim manual:

To add words to your own word list:

zg       Add word under the cursor as a good word to the first
         name in 'spellfile'.  A count may precede the command
         to indicate the entry in 'spellfile' to be used.  A
         count of two uses the second entry.

         In Visual mode the selected characters are added as a
         word (including white space!).
         When the cursor is on text that is marked as badly
         spelled then the marked text is used.
         Otherwise the word under the cursor, separated by
         non-word characters, is used.

         If the word is explicitly marked as bad word in
         another spell file the result is unpredictable.


zG       Like "zg" but add the word to the internal word list
         |internal-wordlist|.


zw       Like "zg" but mark the word as a wrong (bad) word.
         If the word already appears in 'spellfile' it is
         turned into a comment line.  See |spellfile-cleanup|
         for getting rid of those.


zW       Like "zw" but add the word to the internal word list
         |internal-wordlist|.

zuw
zug      Undo |zw| and |zg|, remove the word from the entry in
         'spellfile'.  Count used as with |zg|.

zuW
zuG      Undo |zW| and |zG|, remove the word from the internal
         word list.  Count used as with |zg|.

On the command line:

:[count]spe[llgood] {word}
         Add {word} as a good word to 'spellfile', like with
         |zg|.  Without count the first name is used, with a
         count of two the second entry, etc.

:spe[llgood]! {word} Add {word} as a good word to the internal word list,
         like with |zG|.


:[count]spellw[rong] {word}
         Add {word} as a wrong (bad) word to 'spellfile', as
         with |zw|.  Without count the first name is used, with
         a count of two the second entry, etc.

:spellw[rong]! {word}   Add {word} as a wrong (bad) word to the internal word
         list, like with |zW|.

:[count]spellu[ndo] {word}
         Like |zuw|.  [count] used as with |:spellgood|.

:spellu[ndo]! {word} Like |zuW|.  [count] used as with |:spellgood|.

For more help on spell in vim, type :help spell or :help spell-quickstart

You can follow this guide to integrate openoffice and thunderbird dictionaries: http://hektor.umcs.lublin.pl/~mikosmul/computing/tips/mozilla-thunderbird.html

I don't know your text editor, but if it supports myspell dictionaries the procedure is very similar.