First of all,Aliens will probably have diffrent vocal cords and eyes(most of them,i believe)so the idea that English could be a Lingua Franca is kinda naive..I'm almost certain (and i have reasons to believe it) that there are diffrent "inteligences",not just human inteligence.And diffrent instincts,so what follows:diffrent kind of logic.
There are two solutions to your problem:
I'm not talking about any mumbo jumbo or Jedi Knights,but mind reading technology that is theoretically possible.A device could read your brain waves and transmit it (like a phone call of sorts)to another device of alien lifeforms.This way you could "see" or "feel" what they want to communicate.There are two diffrent versions:
1.Translation of brainwaves into words/sounds of an alien,something like a speaker that will tell an Alien what you thought of.It may be problematic:remember,aliens may be asexual,have diffrent genders,or just completely diffrent set of instincts,so it may still sound nonsensical for them.I guess it also depend on the translation devices.Would they be able to translate everything into another laungage ?The answer is yes when the type of species is similar to humans.We may use similar things here on Earth in 100-200 years or so.
2.Translations of "feelings".This is probably far-fetched,and i cannot see how it would work from the scientific/Engineering perspective.However,when this mind reading or "telepathic" technology is perfected,someone's thoughts could be "translated" into visions or feelings.You could suddenly underrstand what an alien wants and feels like about particular subject.If you want to make it cooler and more mysterious,it could work like a VR of sorts.You would be taken to a virtual world where you could experience the same senses,smells,pain etc.This way you could really understand other species.
Lets call those devices "telephators".Also,note that this all assumes that FTL travel is possible.Without it,it is impossible to keep track of the telephator technology,as those devices need to be compatible with each other.But with FTL a common system could be used.You could think of a fancy name for it and it would work like a "telephatic internet"of sorts.
Inspired by a videogame called "Mass Effect".Imagine an ancient civilisation that has spread all over the galaxy and has left structures with a written laungage(or something else)in many star systems.Because it is a dead laungage,it never changes,it is used in interspecies communication and it is "standarized"for this purpose,and no one uses it in daily life.You get the picture.
This version assumes that Alien species are at least remotely similar to homo sapiens,and even when they have 6 hands or tentacles ,they can at least see a writing system.Note that an Alphabet, Sylabic Alphabet or Abjad is a poor choice:it has to be an iconographic/logographic system like Egyptian hieroglyphs or Chinese Hanzi,where every symbol has a meaning.Memorizing like 100 000 diffrent symbols poses no chalenge for human-like civilization,as you have computers everywhere and they will be able to upload new knowledge straight into their brain implants (or AR glasses or whatever).
If you want your laungage to be spoken,this complicated things.Inn this situation i would go for a Japanese-inspired way of writing.In Japanese,you can write everything in two diffrent versions of "Kana".In essence,they are syllabic Alpabets (one symbol,one syllable)Katakana is used for loan words ,foreign names,countries,plants and animals.Hiragana is used for everything that cant be written with Kanji (Chinese symbols used for Japanese).So majority of words that you see in this laungage are written with kanji,but in the same line you see a lot of Kana as well.
For our purposes,Kanji-like system could be used for species that want/must communicate only through written laungage (they could call those symbols in their own respective laungages,like Chinese read kanji diffrently than Japanese).And kana-like system for sounds....However,it still leaves the problem of deciphering those sounds when we first see them.An recording or some "biological scheme"(a plan of their bodies/genes that would show us how their communication worked)is needed.
In theory,other ways of communication can be found in those "prothean ruins".If a lot of these "dicitionaires"were spread across the Milky Way,they would be seen as the best standarized Lingua Franca (or a set of Lingua francas).
Later if i have more time i will review this answer in case i made some spelling mistakes,and maybe i will add an idea or two.