Astorga to Santiago would be perfect in my estimation. There are several wonderful stages up through the mountains. I walked Leon to Santiago in thirteen days with two days in Astorga. two of my favorite stages are on this route..Cruz de Ferro and O’Cebreiro. Check out the blog below.
https://2016jaxcamino.blogspot.com/
The Portuguese may work also, but you may have bus/train your first day out of Porto. I think this was 12 days with some short walks that could have been combined.
https://2018jaxcamino.blogspot.com/
I hope to be on the Primitivo starting in mid September, so we may cross paths.
Language is not a barrier as most Europeans speak great English. A little Spanish always helps when booking rooms, and French was handy on the Portuguese.
Don’t worry about trying to do a “compete” route. Where you start is a personal choice…there are no rules except for last 100km.