I dont know about civil engineering, but the salary seems low for a qualified person working in Switzerland. That said, as you will see from other threads, it is still an above-average salary in Switzerland.
I guess, the equivalent amount converted into pounds or euros, represents a really decent salary in the UK or Eurozone - so I can see why the company is offering you this.
I guess the questions for you are:
how quickly you want to move over to Bern?
how important money is for you, as opposed to being with your girlfriend (assuming together you have enough to live off)?
and how strongly you rate your chances of finding a better paid job with a different company.
Assuming there is no minimum term in your contract, you could always accept the job, then work on your German whilst you are here and then apply for other jobs and move. With a EU passport and the 5-year B Permit you should get with it, you can change jobs without any problem. However, bear in mind that any new employer will probably ask your existing salary, and therefore may also try to 'underpay' you.
In any event good luck.
Plus, I hope you realise the Gold Coast and Bern are worlds apart