I am not sure there is an exact equivalent in English.
In the British Army there was originally only one major per battalion. Later in the wars a second major was authorised. As a result the 1792 Regulations only mention "the major". However the 1824 Regulations, published as a result of experience during the wars refer to the first major and second major. These were not ranks but just a reflection of their respective seniority (ie an appointment rather than a rank).
There are still vestiges of this system in some modern British Army units. Modern cavalry squadrons (actually armoured today) are commanded by a major with a captain as squadron second-in-command but also have a second captain.
In both cases the "second" officer is not an assistant to the first but has separate duties.