This version is longer but should work with most regional settings

="End date is: "&YEAR(A1+LEFT(A2;2)*7)&"-"&TEXT(MONTH(A1+LEFT(A2;2)*7);"00")&"-"&TEXT(DAY(A1+LEFT(A2;2)*7);"00")&" (incl. "&A2&")"

Note: by using LEFT(A2;2) you only take 1, from 1,5 thereby adding only one week not one and a half - not sure that's your intention