Supported Microsoft formats are Spreadsheets (.xls) and Excel Workbooks (.xlsx).
.xlsx is the default Excel 2007 and later workbook format.
Good to know
POEditor parses 5 columns (A-E), beginning with the first row. The order is term, translation (optional), context (optional), reference (optional), comment (optional).
On export, if a Default Reference Language is set on the project, an extra column is added to the file with the strings in this language (column F). On import, the 6th column is ignored.
Since POEditor accepts only one translation for each term, work with plurals is not possible in the case of MS Excel files.
Official Microsoft Developer Network website: