I don't want to try to draft a larger comprehensive answer now considering it's 3AM but for the sake of others who may come in my stead overnight or myself tomorrow afternoon if no one has gotten to this question by then, I think you may need to specify your question a bit more. More specifically, what part of the 18th century are we talking about here? Are we talking about pre-Fredrick the Great (really the 7 Years' War, so, 1700-1763), the period between the 7 Years' War and the Napoleonic Wars (1763-1792), or the First Coalition War (1792-97) to the beginning of the Second Coalition War (1799-1801). Whichever period you choose, doubly so when speaking about the Napoleonic Wars with particular respect to the French, can yield you some pretty separate answers.

The over generalized and incredibly nuance lacking overview of the question is that for the vast majority of the 18th century, outside of uniforms and traditions, there really was not a whole lot of difference in any official way. There are some special cases and minute details (line depth would fluctuate between 2 and 3 lines but would hardly be consistent enough to consider a doctrinal difference) that are certainly open for consideration but, as a whole, in the early and middle 18th century it is, unfortunately for the excitement of this question, pretty same-y.

If you want further reading about this topic I'd highly recommend H.W. Koch's work The Rise of Modern Warfare: 1618-1815. Be warned it is incredibly dense, basically a textbook, and pretty dry at times; however its sheer quantity of information can't be ignored if you're interested in this period.

Sorry about having no sources at the moment, I'll look for some later. I studied this in school, my main interest is between 1680 and 1830. During that time, much line infantry was extremely similar. Not much armor was worn, so the clothing of the people did not matter at all. Different areas had different tactics, which led to different doctrines and strategies being used. For example, eastern Europe still fought bow-wielding tartars, and incorporated a lot more cavalry into the army than the rest of Europe did. This meant that their doctrine was more based on cavalry support, with thicker lines and spaces between regiments.

Western Europe, mostly France, however, was more based on artillery and balance. Lots of guys lined up and shot at each other then ran up and charged each other. All while cavalry ran around the edges and shells rained from behind it all.

Central Europe, Prussia mostly was very infantry based. Line infantry was widely supplemented with longer ranged light infantry who used finer muskets. You may have also heard of Jaegers. Jaegers used rifles, and were the first units to do so widely. Rifles were extremely accurate for the time, and much longer ranged than muskets. Prussian doctrine was based on using these finer infantry troops to their full potential.