Is it permissible to combine two salaries from the state if one works diligently and devotedly in both jobs, and neither affects the other, such as when one is a teacher and also works for another governmental entity?

There is no objection to combining two jobs in the government sector, unless the government prohibits it, due to the generality of Allah's Almighty saying: "O you who have believed, fulfill [all] contracts," and the saying of the Prophet, peace and blessings be upon him: "Muslims are bound by their conditions in what is permissible."