"He deletes his data."
Translation:Er löscht seine Daten.
How come sometimes translation for data is used Wert and sometimes Data?
I would normally translate Wert as “value”. In the “how much sth is worth” sense (“worth” and Wert come from the same root actually), but also that of “a single point of data”. So “data” may sometimes be translatable as “Wert”.
"data" in English is usually always plural and uncountable -- it can refer to one item of data or many items of data.
So it could be Er löscht seinen Wert (his value, his data item -- masculine singular accusative) or Er löscht seine Daten (his data, his data items -- plural accusative).
What is not possible is seinen Daten; if you type that, you may get seinen Wert suggested as a correction, as the checker thinks you're more likely to get the first word right and the second one wrong rather than the other way around.
But, how is one supposed to know if the statement is referring to Daten, or Datum? It could be either. Maybe he deleted a single piece of information.
The singular of "data" in English is "datum", but in practice, the singular is very rarely used -- and that is the same in German.
The German word Datum essentially always means a calendar date, not a datum as in a piece of information.
The plurals "data" (in English) and Daten (in German) are most frequently used when the meaning is "information", regardless of the quantity of information.
If all a company knows about me is my name, then deleting that one item of information is deleting meine Daten from that company's website. I wouldn't say mein Datum or "my datum".