Thanks for your posting and using Aspose.Cells for Java.
It seems your issue is related to fonts. Please set the font directory first and see if it resolves your issue.
In order to set the font directory, please use the following code. Please
place the line at the beginning of your code before creating a workbook.
CellsHelper.setFontDir(“c:\windows\fonts”); //change the path to your font directory.
In case of Linux, use the directory path according to Linux syntax. e.g