If you are look for mp3 audio files to help you learn Spanish, you can create the mp3 files by yourself using speech synthesis software
panopreter, but it is not an Android app, it's a Windows application. you also need to install a Spanish voice on your Windows operating system, for example,
Cereproc Spanish voice, thus the software can convert any Spanish text into wave or mp3 file, later you can import the mp3 files into you phone. By default, there is only English voice on Windows.