OmniTranslator can open a translation window that will translate whatever is on the screen, under the mouse.
In the following screenshots, the popup shows the text captured in grey and the translation in the white zone below. If additional information is captured (such as information tooltips), this is also translated.
Translation in Excel:
Translation in a Windows menu:
Translation in a pdf document:
Note: Omni Translator only recognizes text. If the file is a scanned document, Omni Translator will not be able to translate it.