Not so.much lose a common tongue but an example will be like pigeon English or English as second language ask someone who speaks that to read a book and translate it into action the results are not the same as proper English. Higher english the technical stuff will be lost, many abstract ideas that affect how things work will become lost.
One example will be how do you explain things in geometry to someone without proper English skills? Physics ? There is a reason the countries like England did not allow conquered people for centuries to learn such simple things as a comprehensive scope of language. If you can’t explain an idea how do you share it? Improve on it?
Also there is a distinct lack of read and do many of new generation this is not a mode they possess,no YouTube and you have mindless idiots who top searches on homedepot is how to change light bulb and how to read tape measure.
As for things like powder there is powder recipe 1/3 each and the Queens recipe which is almost lost secret to make same thing but much more powerful. Think local chef vs a celebrity chef it’s not the ingredients but the skill combining them and how it’s done that makes results between I can’t eat this to this tastes like ambrosia.
Most knowledge is so compartmentalized that few can make a complex item from true raw. Example make a steel knife from iRon you find. that is simple imagine something as complex as a radio.
I can make ground up chemical compounds to rarified substances but even with knowledge if I had equipment and raw materials in quantities I needed it would take YEARS to make some things. I stock alot of what I call starters and know where to get more from common items but to do some things would take a workforce of 100s of people let alone support staff. These things will be lost because by 3Rd gen it will be like a fairytale that we had great metal.birds that could fly. Metal tubes that could wipe out a country with a push of a button from 1 years sail away in less than an hour.
I think other than basics all we could hope to carry through is our art and our warning of which path not take. We all have heard the cautionary tales from the pas in many forms and look we are still here arent we?