Excel Translate

Translate spreadsheet cells with a worksheet formula, using a model that runs on your own machine.

What it is

Excel Translate is an Office Add-in for Excel for Mac that registers two custom worksheet functions in the XLT namespace:

=XLT.TRANSLATE(A2,"de")
=XLT.TRANSLATE(A2,"en","de")
=XLT.TRANSLATE_RANGE(A2:B10,"fr")

The formulas call a small local HTTPS host written with the Python standard library. That host serves the add-in’s static files to Excel and proxies translation requests to LM Studio’s OpenAI-compatible local API, using whichever model you have loaded there.

Why

Formula-first

Translation is a cell function, not a task-pane button. It recalculates and fills down like any other formula.

Stays on your machine

Text is sent to LM Studio on localhost. There is no cloud translation provider and no API key to sign up for.

No build step

The add-in is plain HTML and JavaScript. The server is Python standard library only, with no third-party packages.

Bring your own model

Any chat/instruct model loaded in LM Studio works. Pin one with LM_STUDIO_MODEL or let the proxy auto-detect the first model from /v1/models.

How the pieces fit

Excel loads the add-in from https://localhost:3000 using a sideloaded manifest.xml.
web/functions.js implements TRANSLATE and TRANSLATE_RANGE and POSTs to /api/translate.
scripts/dev_server.py receives that request, builds a translation prompt, and calls LM Studio’s /v1/chat/completions.
The translated strings come back to the cell (or spill across a range).

See Architecture for the full request path, and Formula Reference for argument semantics.

Requirements

macOS with Excel for Mac that supports the Custom Functions runtime (CustomFunctionsRuntime 1.1)
Python 3.12+ (or Docker, which is the documented default path)
LM Studio with its local server running and a model loaded
A self-signed localhost certificate that you generate yourself — see Installation