How do the spanish feel about the intervention of foreigners in their civil war?

There was intervention on both sides of the civil war, each side appreciated the aid they received. You had a lot going on here....... the communists are aiding the communists, and then it comes to the forefront that the communists want to abolish religion and things change. The loyalists attract support from democratic nations....... the facist garner assistance from Germany and Italy. It's a mess......

It is Politics

Do you mean how did the Spanish people feel, or those who decided to go to war?

In the first instance I doubt anyone asked the people.

In the second, both sides needed arms, and those came from outside the country along with troops and advisors.

They still fight and bomb in Spain now.