Speaking as a potential hirer (in the sense that I manage a technical team and regularly look at both junior and senior dev resumes):
- if your CV only lists 1 language/framework and it’s one I’ve never heard of, I’m not likely to keep reading.
- if you have 8 years of experience in the same company, I expect to see concrete achievements and ideally that you moved up the ladder in 8 years (more responsibilities, changing teams, a new job title for instance)
- not something I insist on, especially for a senior profile, but which can have a positive impact on a candidature: is there a portfolio website or a GitHub profile on the CV/cover letter? This allows me to see what language(s) the candidate has used in the past, take a look at their coding style, check the commit history (e.g. a repo with 1 huge “upload project” commit and no other activity smacks of someone who’s never used git before)
Given the shortage of devs, you’ll find a new position. How fast you find it, and how senior it is, is up to you. I encourage you to pimp your 8 years of experience to show portable skills (problem solving, autonomy, system design...) rather than proprietary tech knowledge, and a capacity to grow and learn (i.e. show your progression during these 8 years).
Then, assuming this isn’t already the case, pick up a popular language and work on a few projects in your spare time. This will enable you to brush up on your CS skills and programming paradigms, especially if the language you use at work is primitive: do some OOP, try your hand at FP, asynchronous or parallel computing, etc. Make sure the code is clean and commented, and throw in some unit tests. Commit to github like a sane person, and add the relevant language and frameworks on your CV. Bam! Suddenly you’re a developer with 8 years of experience who happens to know a weird language.
Of course this is only good enough to get through the automated CV analysis and the first interview. But in that interview you have the opportunity to explain what you accomplished in 8 years (maybe pointing out how solving tough business problems with an antiquated language is even more impressive than with the bells & whistles language du jour). You can point out that you want more and that’s why you work on side projects with a modern language (which incidentally is part of the company’s stack). And since you’ve been coding on your free time you’re hopefully up to date on basic data structures and algorithms and you’ll pass the whiteboard tests brilliantly.