In case you didn’t know, you can slipstream server pack 1 (or the latest SP) of a language pack into the RTM service pack installation point, creating a single install point for each language pack include includes SP1.  You may think, big deal, I’m saving one installation.  That’s true, but if you have a a medium or large farm, it cuts the number of items you need to install by half, which can add up over time, especially if you have a dev and QA/staging environment you keep in sync.  Unfortunately, you can only do this per language, so you still need to do one install per language, but every little bit helps.

For WSS Language Packs (example here is for the Spanish language pack):

1. Download the WSS Language Pack RTM and SP1 packages for the languages you are installing to C:/WSS_LPs/Spanish.
2. Extract the RTM package to a folder using the following command:

   C:\WSS_LPs\Spanish>SharePointLanguagePack.exe /extract:C:\WSS_LPs\Spanish\

3. Extract the SP1 package to the UPDATES folder inside your language folder, using the following command:

   C:\WSS_LPs\Spanish>wssv3lpsp1-kb936988-x86-fullfile-es-es.exe /extract:C:\WSS_LPs\Spanish\Updates

4. Install the language pack with SP1 by executing C:\WSS_LPs\Spanish\setup.exe

For MOSS Language Packs (example is for the Spanish language pack):

1. Download the MOSS Language Pack RTM and SP1 packages for the languages you are installing to C:\MOSS_LPs/Spanish.
2. Mount the ServerLanguagePack.img file using a virtual CD drive application
3. Copy all the contents from the mounted volume to C:\MOSS_LPs\Spanish\
4. Extract the SP1 package to the UPDATES folder inside of your language folder, using the following command:

   C:\MOSSLanguagePacks\Spanish>officeserverlp2007sp1-kb936984-x64-fullfile-es-es.exe /extract:C:\MOSS_LPs\Spanish\Updates

5. Install the language pack with SP1 by executing C:\MOSS_LPs\Spanish\setup.exe