Can iOS8 QuickType show suggestions in more than one language?
Yes, this is possible, although not automatically. There's currently no way for iOS to detect the language of the message, but you can use multiple keyboards to show predictions in a different language of your choice.

To do this, go to Settings > General > Keyboard > Keyboards. This screen shows a list of keyboards set up on the device. You can use the Add New Keyboard... link at the bottom of the screen to add additional keyboards. The keyboards are ordered by language and locale (e.g. English (Australia)) - and there's also the Emoji keyboard there, for adding smileys and other funny icons to your messages.

Depending on the keyboard, there might be multiple layouts (QWERTZ, QWERTY, AZERTY), which can be switched from the list of selected keyboards by opening the keyboard's details.

Once you have selected an additional keyboard, you will see a new globe icon at the bottom left of the keyboard. Pressing the globe icon will switch to the next keyboard, holding the icon for a moment will show all available keyboards, and will also allow to enable/disable the predictions.

Switching to the English keyboard will show predictions in English language, while switching to German will show predictions in German language. The Emoji keyboard doesn't show any preditions :-)