The word 'engineer' in English has multiple senses, so many non-technical people don't fully appreciate the difference between 'a person who works on machines' and engineer in the professional sense. In some languages and jurisdictions, there is a very clear definition of 'engineer', especially where it is a reserved title.
I don't think there is a single answer as to what specifics are required to make an Engineer when used in the conventional (proper) English sense. The 1961 Conference of Engineering Societies definition makes no reference to a specific qualification:
Definition of Engineer on Wikipedia
I would expect a first professional degree (e.g. BSc, BEng), full membership of a professional organisation (e.g. IET, IEEE) and possibly some relevant experience.