Usability
Interface 
User-friendliness/complexity of the tool´s interface
Simple
Time efficiency Time needed for mastering the „how-to“ of the tool and a production of a task
High
Interface language(s) The number of languages in which the tool is currently available/adaptable to
English, Spanish, French, German, Italian, Greek, Brazilian Portuguese, Romanian, Polish, Hindi, Ukrainian, Russian, Corean, Hungarian, Turkish, Czech, Thai, Chinese, Arabic, Chinese, Japanese, Indonesian, Vietnamese, Dutch
Respect for privacy Does the tool require registration? Who can see my data? Can I remain anonymous?
Medium. Duolingo collects and collects information necessary to process purchases, provide customer support, and optimise the site. Duolingo might share personally-identifiable information with third parties if it is “reasonably necessary to offer the Service” but it does not sell it. The policy mentions the use of cookies but does not provide extensive details on security measures. Duolingo mentions lawful bases for processing personal information under GDPR, to which it complies, including consent. See more here..
Saving work for future use Possiblity to save your or others´ work for reuse/reproduction
Yes
Tailorability (If so, how?) Possibility of the tool to be used for a range of different activities (e.g. to what extent you can organize a project assignment with a central activity based on this tool)
No. The user must follow the pathway set by the app.