I never understood this argument. To use a function you have to look up its name anyway*, so what does it matter which language inspired the name? I wouldn't mind if sum() was known as hezrtsh() as long as it was consistently so, I could have a chance of learning it.
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* I still sometimes struggle to remember if it's average() or mean() and whether it's count() or length() -- different programming environments use different names. So even as an English speaker, I have to look up the word for each specific programming environment.
There are few obscure functions that have parameters and those parameters can come in home language - so they will stop working. Also there are some issues with charts.
In general Excel is made for corporations and people from different countries send each other files all the time.
However it would be nice to be able to dynamically switch language. There are few websites that translates formulas.
The cell formulas were actually stored in Reverse Polish Notation with each function represented as a number. The actual ASCII you entered was never stored anywhere.
It's probably the most interesting and amusing file format detail I ever stumbled upon.
The name you type in - say - a German version is saved as a "function number" on file.
When the file is opened in - still say - an English version, these "function numbers" are rendered as the English names.
I think only because Excel is not, at its core, a programming tool.
For programming languages, English is universal. You are pretty much forced to learn English in order to take your first programming steps, and -- as a non-native speaker -- I find this is a good thing. This way, we have a lingua franca of programming.
It's not because of a particular love of English. It is what it is. I would have welcomed French or Italian or whatever had it been the lingua franca instead. I would probably NOT have welcomed Japanese or Chinese written with ideograms because those writing systems are completely extraneous and hard to match for my Western brain, but anything else is fair game.
A "Tower of Babel" situation would be the worst.