oracle/graal · error · IllegalArgumentException

unsupported locale: %s

Error message

unsupported locale: %s

What it means

Thrown by PythonLocaleData.getLocaleData when the encoding part of the locale string does not name a charset known to the JVM. After splitting on '.', Charset.forName(encoding) throws UnsupportedCharsetException or IllegalCharsetNameException, which the method converts into IllegalArgumentException('unsupported locale: ...').

Source

Thrown at regex/src/com.oracle.truffle.regex/src/com/oracle/truffle/regex/flavor/python/PythonLocaleData.java:93

    private final CodePointSet wordChars;
    private final CodePointSet nonWordChars;
    private final byte[] caseFolding;

    public static PythonLocaleData getLocaleData(String locale) {
        if (locale.equals("C")) {
            return createCachedLocaleData(false, Charset.forName("US-ASCII"));
        } else {
            int dot = locale.indexOf('.');
            if (dot == -1) {
                throw new IllegalArgumentException("malformed locale: " + locale);
            }
            String language = locale.substring(0, dot);
            String encoding = locale.substring(dot + 1);
            try {
                return createCachedLocaleData(language.startsWith("tr_"), Charset.forName(encoding));
            } catch (UnsupportedCharsetException | IllegalCharsetNameException e) {
                throw new IllegalArgumentException("unsupported locale: " + locale);
            }
        }
    }

    public CodePointSet getWordCharacters() {
        return wordChars;
    }

    public CodePointSet getNonWordCharacters() {
        return nonWordChars;
    }

    public void caseFoldUnfold(CodePointSetAccumulator charClass, CodePointSetAccumulator copy) {
        charClass.copyTo(copy);
        int iFolding = 0;
        for (Range r : copy) {
            iFolding = caseFoldingBinarySearch(iFolding, r.lo);
            while (iFolding < caseFoldingSize() && caseFoldingFrom(iFolding) >= r.lo && caseFoldingFrom(iFolding) <= r.hi) {

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Use a canonical, widely-supported encoding in the locale string, ideally '.UTF-8'
2. Map environment encoding aliases to canonical Java charset names at the call site (e.g. 'cp1254' -> 'windows-1254', 'ANSI_X3.4-1968' -> 'US-ASCII')
3. Fall back to 'C' when the encoding cannot be resolved and locale-specific behavior is optional
4. If a legitimate charset is missing, run the JVM with full charset support (include jdk.charsets)

Example fix

// before
PythonLocaleData.getLocaleData("tr_TR.cp1254"); // unknown name

// after
PythonLocaleData.getLocaleData("tr_TR.windows-1254");

boolean isSupportedLocale(String locale) {
    if (locale.equals("C")) return true;
    int dot = locale.indexOf('.');
    if (dot <= 0) return false;
    try {
        java.nio.charset.Charset.forName(locale.substring(dot + 1));
        return true;
    } catch (java.nio.charset.UnsupportedCharsetException | java.nio.charset.IllegalCharsetNameException e) {
        return false;
    }
}

When it happens

Trigger: Calling getLocaleData with a locale whose suffix after '.' is not a valid/installed charset, e.g. 'en_US.US-ASCII-TYPO', 'xx.BOGUS', 'tr_TR.905' (bare codes the JVM does not resolve), or an encoding not present in the JVM's charset providers.

Common situations: Guest Python code reading LC_ALL/LC_CTYPE from a Unix environment and forwarding values whose encoding aliases the JVM does not know (e.g. 'ANSI_X3.4-1968', 'cp1254', numeric codes); containers with unusual locale settings; JVMs where extended charset support (jdk.charsets) is not on the module path.

Related errors

• malformed locale: %s
• nargs not allowed
• illegal type for element %s: %s
• %s missing element %s
• Not an annotation type

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/95d66586bc7bfd5c. Report an issue: GitHub.