Similar to scholarships, the range of job opportunities will greatly increase if a student has acquired an at least basic proficiency in German. This does not mean that English-only speakers are without options, however. On the one hand, there are “traditional” student jobs that require only a minimum or even no language expertise, as, e.g. sometimes in gastronomy. On the other hand, Tübingen is an international city, not only due to its student clientele, but also because of the strong economy in the region, and thereby the presence of international companies where German language proficiency is a less important factor. Especially larger technology, electronics, media, engineering, or IT companies that rely on English as their lingua franca might have jobs for students who know little German. In this regard, it might also be useful to have a look at Stuttgart and its surroundings (~50km from Tübingen and easily accessible by public transport) where many big technology companies have branches.
Furthermore, the Praxisportal of the University of Tübingen also lists jobs outside of academia (and allows searching for English-only jobs):
The Federal Employment Agency offers a job search machine (currently only in German) for a variety of employment types:
Although in this page there is no option to specifically search for student jobs, using terms like "Minijob", "Mini Job", "Studierendenjob", "Studentenjob" or only "Student"/ "Studierender"/ "Studierende"/ "Studenten" can output some viable results. Minijobs are a type of marginal employment (usually part-time and low wage; they can also be only short duration jobs). They are tax-free, without social charges, and often compatible with student working conditions. Multiple minijobs can be combined, provided the overall income does not exceed 538€ per month. If in doubt about the conditions, please contact the Immigration Office.
Another option could be to approach a company you are interested in working for directly and ask for any vacancies for a student with (your) specific qualifications.
Please note that international non-EU students are prohibited to work on a freelance/self-employed basis unless they have obtained permission from the Immigration Office.