If you program in C++/Java and all your libraries handle locale correctly, it's doable. A bit more difficult in languages and libraries written by people who aren't even aware of the concept - of which there's plenty. Impossible if you're dealing with customers or managers who don't understand the concept of "data type". The latter is, for example, why the problem from TFA exists in the first place - i.e. Excel being stringly typed, and eagerly converting data into your system locale.
And then, there's the problem of users - whatever locale they have set in their system were most likely not set by them, and are often misaligned with what they're naturally using.
There's a lot of bugs and issues happening to people every day that could be removed if major software vendors said, "sorry, the only allowed input format for date is ISO8601, and dot is the only valid decimal separator; take it or leave it".
And then, there's the problem of users - whatever locale they have set in their system were most likely not set by them, and are often misaligned with what they're naturally using.
There's a lot of bugs and issues happening to people every day that could be removed if major software vendors said, "sorry, the only allowed input format for date is ISO8601, and dot is the only valid decimal separator; take it or leave it".