If you change the category code of the double quote character then you can define a macro that typesets "test" as ``test''. In doing this, the only downside that I can see is that you will run into problems if you forget a closing quote. It is also not unlikely that this will cause havoc with some packages -- for example, double quotes are used by tikz so this will almost certainly not work if you want to use this in documents that also uses these features of tikz. You'd really be better off using the recommended quoting style of LaTeX, which is to use repeated left and right quotation marks instead of double quotes. A global search and replace in any decent editor that supports regular expressions should fix your current document.
For completeness I have added a \quot command to access the "real" double quote character and I have checked that accents like \"a still work as expected.
Here's the code:
\documentclass{article}
\newcommand\quot{"}% allow access to the real double quote
\catcode`\"=13 % change the category code of "
\def"#1"{``#1''} % and make "stuff" expand to ``stuff''
\begin{document}
"test"
Universit\"at
You can also write \quot test\quot
\end{document}
and here is the output:

csquotesand use\enquote{I am a wombat}in your text. – Johannes_B May 09 '19 at 05:0320%the"should not be used, use\`` and''– David Carlisle May 09 '19 at 06:47