There are a growing number of threads with custom CAB updates.These CAB's are meant for custom ROM's on devices with unlocked bootloaders (HSPL). In that case they would return error 800B010A: "A certificate chain could not be built to a trusted root authority." The list in this thread will only contain the official updates from Microsoft and the official OEM updates, which can be applied on stock ROM's.I want to ask other people to provide additional links for official updates.
If you want to catch language-packs, you can edit the registry with a high-privilege registry editor like WP7 Root Tools, by going to "HKLM\MUI\Available" and add registryvalues for the languages you need before you do the update through Zune. The name of the value should be the 4-digit hex language-code (look here for different language-codes).
The content of the value should be the description of the language.
Then startup Wire Shark and monitor you internet connection in promiscuous mode. You'll also see which cab-files will be downloaded for your language packs.
A lot of info in this thread is based on the work of Da_G, xboxmod and Yuki XDA. To add OS updates and languages we need CAB files, which are update-packages, that can be flashed to your phone, just like a normal update by Zune would work.
The advantage with offline updates is that you can download and apply them at any time and you can add additional languages as you like. So if you add these packages and you hard-reset your phone, the update will remain on your phone, just like a normal phone update would.
For these CAB-updates you don't need to be unlocked in any way!
You can always apply these updates to your WP7 device.
After making Android JB 4.1 available for these smartphones, we received feedback on a few issues within the build.
We’re keen to ensure that all our software is as good as it can possibly be, so we’ve addressed these & improved on a few things…