Issues with altair localization

[larsrinn]

Describe the bug

It seems like it's not possible to show altair charts when localization is enabled as shown here: https://altair-viz.github.io/user_guide/customization.html#localization

After the alt.renderers.set_embed_options(format_locale="it-IT", time_format_locale="it-IT") is executed, simply outputting the chart (without using mo.ui.altair_chart) doesn't show anything. When I wrap it in the UI method, I get an error message:

t is undefined
PO@http://localhost:2718/assets/index-BR3wLmMq.js:63:22132 Hce@http://localhost:2718/assets/index-BR3wLmMq.js:63:18343 yue@http://localhost:2718/assets/index-BR3wLmMq.js:63:28244 ux@http://localhost:2718/assets/index-BR3wLmMq.js:63:28294 Bn/<@http://localhost:2718/assets/VegaLite-lc7CRpzR.js:189:2511 Bn@http://localhost:2718/assets/VegaLite-lc7CRpzR.js:189:5488 

Interestingly, if I apply vegafusion as data transformer before setting the locale, the error message disappears and charts are shown. However, localization is not applied

Will you submit a PR?

• Yes

Environment

Details

{
  "marimo": "0.13.11",
  "OS": "Darwin",
  "OS Version": "24.5.0",
  "Processor": "arm",
  "Python Version": "3.13.1",
  "Binaries": {
    "Browser": "136.0.7103.114",
    "Node": "v20.18.1"
  },
  "Dependencies": {
    "click": "8.2.1",
    "docutils": "0.21.2",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.8",
    "narwhals": "1.40.0",
    "packaging": "25.0",
    "psutil": "7.0.0",
    "pygments": "2.19.1",
    "pymdown-extensions": "10.15",
    "pyyaml": "6.0.2",
    "starlette": "0.46.2",
    "tomlkit": "0.13.2",
    "typing-extensions": "4.13.2",
    "uvicorn": "0.34.2",
    "websockets": "15.0.1"
  },
  "Optional Dependencies": {
    "altair": "5.5.0",
    "duckdb": "1.3.0",
    "nbformat": "5.10.4",
    "openai": "1.82.0",
    "pandas": "2.2.3",
    "polars": "1.30.0",
    "pyarrow": "20.0.0",
    "loro": "1.5.1",
    "ruff": "0.11.11",
    "sqlglot": "26.19.0"
  },
  "Experimental Flags": {}
}

Code to reproduce

import marimo

__generated_with = "0.13.11"
app = marimo.App(width="medium")


@app.cell
def _():
    import altair as alt
    from vega_datasets import data
    import marimo as mo

    source = data.stocks.url
    chart = alt.Chart(source).mark_area().transform_filter('year(datum.date) == 2009').encode(
        x='date:T',
        y=alt.Y('price:Q', axis=alt.Axis(format="$.0f")),
        color='symbol:N'
    )
    chart
    return alt, chart, mo


@app.cell
def _(chart, mo):
    mo.ui.altair_chart(chart)
    return


@app.cell
def _(alt, chart):
    #alt.data_transformers.enable("vegafusion")  # uncomment to avoid error message
    alt.renderers.set_embed_options(format_locale="it-IT", time_format_locale="it-IT")
    chart
    return


@app.cell
def _(chart, mo):
    mo.ui.altair_chart(chart)
    return


if __name__ == "__main__":
    app.run()

[Light2Dark]

It seems we aren't resolving the locales properly, a temp workaround is to use the vl-convert library (pip install vl-convert-python)

import vl_convert as vlc

alt.renderers.set_embed_options(
   format_locale=vlc.get_format_locale("it-IT"), time_format_locale=vlc.get_time_format_locale("it-IT")
)