Hi @Georgiana lovely to hear from you! As @andfraz said you are very welcome to mention your contribution to TWB in your LinkedIn profile 
You can also embed your translator badge in your Proz profile following these instructions.
And you are quite right, we do provide reference letters to our translators 
However to make it fair for everyone, we ask that you first reach certain word count thresholds. To see the thresholds, have a look at our thread on the General Recognition Program.
If you would like access to more tasks in your language pair, you can consider becoming a Kató Verified Translator! This will increase your chances of finding tasks that match your skills, interests and time schedule 
To find out more, please visit this page.
Let us know if you have any questions! 