You're most certainly allowed to edit it. That's one of the cornerstones of all free and open software. However, you must also make your edited version available as source code under the same terms as the original library. That's one of the cornerstones of copyleft licenses (such as the Lesser GPL). Use the software in a free manner, and in return give any ...
You can recover that specific link via the way back machine:
codehaus says from their termination page that you can redirect your projects:
If you would like your projects links redirected then please see our redirector repository - create a sane squashed pull ...
If you click on the link "this post", you will see this page:
It contains more information about the process, including this text:
As previously announced, most of Google Code will become read-only on August 25th, 2015.
We are still working with Google-affiliated projects (e.g., /p/chromium and /p/android) to get them migrated to other tools and ...
The API (and only the API) is under the Apache v2 License, so you can use that under its terms which includes commercial usage; that doesn't make google's TTS open-source though.
Actual access to the API and services requires agreement to further terms from google which are described in the documentation and when signing up for / signing-in to a google ...
The code appears to be legal to use as it's under some sort of permissive license. I read this disclaimer as a hint that Google Maps licensing is separate.
For Google Maps you need to comply with ToS and may be required to pay: https://cloud.google.com/maps-platform/pricing/.
The question could boil down to IMHO:
Can I reuse copyrighted media in some FOSS software?
The key point is to determine whether or not you are authorized in general to do so.
I assume you mean that this app is likely open source itself but it does not matter much. The format of the media does not matter either (it could be a Gif, mp4 or else). And ...