"Erstwhile" as an ajective is "former" or "previous." As an adverb, it is "formerly." "Ersatz" is an imitation, generally inferior. A mnemonic device is the "...while" -- related to time, hence former.
In simplest terms Ersatz means Fake or a Substitute.
Ersatz means being a substitute or imitation, usually of inferior quality. It is used to describe something that is intended to replace or imitate the original.
Erstwhile Records was created in 1999.
Erstwhile means former, previous, or in the past.
An ersatz is something which is made in imitation, as an effigy or substitute for the original.
The Ersatz Elevator was created in 2001-03.
An ersatz swing would be an imitated; or fake swing.
When Joe brought home an ersatz diamond ring, his fiancee threw him out.
Depending on context, Ersatz can be translated as:surrogatereplacementsubstitutesparealternativerefundcompensationreimbursement
Ersatz GB was created on 2011-11-14.
the man was very erstwhile when he walked
Erstwhile Susan was created on 1919-11-16.