I've been with my employer for 5 years and have received a Zwischenzeugnis (translates as "interim evaluation") 2 and a half years ago, when my supervisor changed. I asked for a new one a year and a half ago when my I got yet a new supervisor and was promised one, but only got excuses. I didn't press the point.
In March I asked my new supervisor for one and was told yes. 3 months went by - nothing. I pressed the point and my supervisor (a German) got defensive, finally saying I could have one at the end of the year if I insisted. I went to HR begining of July to ask them to explain to him his legal obligations. But they're overworked and don't have time, other than sending him an e-mail to no effect. Question: should I just drop the issue? I think I'm already experiencing some "retaliation" for what my supervisor seems to think is an intention on my part to look for a better job. This is not the case - I want to stay where I am, but the company is on shaky legs and may not be around in a year or two. In any case, a record of performance is my legal right. But if I get an attorney, that will pretty much be the end of any meaningful work at this company. At my age - 56 - I can't exactly pick and choose a new employer at will.

As they didn't react send them a registered letter and a deadline of 2weeks. Refer to Art. 330a of the Obligationenrecht. After that you can go to court, there is a simplified process for minor cases.
Also consult the following link about labour disputes:
https://www.ch.ch/en/labour-disputes/

If you face retaliation because of it write everything down and look this site up:
http://mobbing-beratungsstelle.ch/mobbing-arbeitsplatz/