Well, it can be a signal of other effects. For example, if it is written in python (or ruby), it probably isn't very fast. If it written in JavaScript (especially with electron), it will probably be a memory hog. If it is written in c or c++, there is a bigger risk of segfaults. If it is written in rust, it probably doesn't have a good gui (at least right now). None of those are garantees though.
And the design of the language can influence the design of applications in more subtle ways, for example projects written in languages that are more difficult to learn, like rust or haskell will attract different developers than projects written in more accessible languages like python and JavaScript. Not that either is unilaterally better.
And if course, if you are going to contribute to an open source project, such as editor, that you use, then the language absolutely matters.
And the design of the language can influence the design of applications in more subtle ways, for example projects written in languages that are more difficult to learn, like rust or haskell will attract different developers than projects written in more accessible languages like python and JavaScript. Not that either is unilaterally better.
And if course, if you are going to contribute to an open source project, such as editor, that you use, then the language absolutely matters.