The aim of this study was to explore differences in oral fluency between native and non-native speech, with a focus on the influence of task type and task difficulty. To reduce the impact of language structure on variability, the study compared High German (HG) and Low German (LG), two closely related languages with similar phonology, grammar, and vocabulary. Native speakers of HG, who had successfully completed a language course in LG, performed eight speaking tasks in both languages. To evaluate the effect of task difficulty on fluency parameters, three of these tasks were presented at different levels of task complexity, which was achieved by varying the availability of relevant information, the pre-task planning time, and the familiarity of the task. Measures of speed and breakdown fluency were obtained from both languages. As expected, LG speech showed lower speed and breakdown fluency compared to HG speech, but this effect varied by task type and task difficulty. We conclude that the assessment of oral fluency through effective variation of task type and task difficulty remains a major challenge for future research.