vielfach
often
Used adverbially: often, many times, on many occasions.
Dieses Problem wurde bereits vielfach diskutiert.
This problem has already been discussed often.

often / multiple
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often
Used adverbially: often, many times, on many occasions.
Dieses Problem wurde bereits vielfach diskutiert.
This problem has already been discussed often.

The word consists of 'viel' (much / many) and the ending '-fach'. This ending means '-mal' (times) or '-fältig' (-fold), as in 'einfach' (simple / single) or 'zweifach' (double / twofold). 'Vielfach' (often / multiple) therefore literally means 'many times' or 'varied'.
Es gibt vielfache Gründe für seine Entscheidung.
There are multiple reasons for his decision.
'Vielfach' (often / multiple) can be used as an adverb (unchanged) or as an adjective (declined before a noun). As an adverb, it means 'oft' (often); as an adjective, 'zahlreich' (numerous) or 'vielfältig' (varied).
Er hat sich vielfach für seine Arbeit engagiert.
He has often been involved in his work.
In its adverbial meaning 'oft' (often), 'vielfach' (often) belongs more to written language or a formal style. It is used less often in everyday spoken language.
Wie vielfach berichtet wurde, steigen die Preise weiter an.
As has often been reported, prices continue to rise.
The combination 'auf vielfachen Wunsch' (by popular request / due to multiple requests) is a very common fixed expression. It means that something happens because many people wanted it.
Auf vielfachen Wunsch wird die Ausstellung um einen Monat verlängert.
By popular request, the exhibition will be extended by one month.
often
'oft' and 'vielfach' can both mean that something happens often or on many occasions. 'oft' is the normal word and very suitable for everyday use. 'vielfach' can be used in a similar way, but it sounds somewhat more factual or written. In conversation, people usually say 'oft'. In reports, explanations, or general statements, 'vielfach' can sound natural.

Bei der Arbeit wurde vielfach gelobt, dass das neue System einfacher ist.
At work, many people praised the fact that the new system is simpler.
Herr Demir arbeitet oft draußen, auch bei schlechtem Wetter.
Mr. Demir often works outside, even in bad weather.