languagetool-org/languagetool · error · IllegalArgumentException

You have to set the source language (as mother tongue) in bi

Error message

You have to set the source language (as mother tongue) in bitext mode

What it means

In bitext (bilingual) mode LanguageTool needs the source language to align the two texts; it is taken from the --mother-tongue option. If --bitext is given without --mother-tongue, main() throws this IllegalArgumentException before any checking starts.

Source

Thrown at languagetool-commandline/src/main/java/org/languagetool/commandline/Main.java:455

    }
    if (languageHint != null) {
      String spellHint = "";
      if (!prg.isSpellCheckingActive()) {
        if (prg.lt.getLanguage().isVariant()) {
          spellHint = " (no spell checking active)";
        } else {
          spellHint = " (no spell checking active, specify a language variant like 'en-GB' if available)";
        }
      }
      System.err.println(languageHint + spellHint);
    }
    prg.setListUnknownWords(options.isListUnknown());
    if (options.isProfile()) {
      prg.setProfilingMode();
    }
    if (options.isBitext()) {
      if (options.getMotherTongue() == null) {
        throw new IllegalArgumentException("You have to set the source language (as mother tongue) in bitext mode");
      }
      File bitextRuleFile = options.getBitextRuleFile() != null ? new File(options.getBitextRuleFile()) : null;
      prg.setBitextMode(options.getMotherTongue(), options.getDisabledRules(), options.getEnabledRules(), bitextRuleFile);
    }
    if (options.isRecursive()) {
      prg.runRecursive(options.getFilename(), options.getEncoding(), options.isXmlFiltering(), options.getLevel());
    } else {
      if (options.isLineByLine()) {
        prg.runOnFileLineByLine(options.getFilename(), options.getEncoding(), options.getLevel());
      } else {
        prg.runOnFile(options.getFilename(), options.getEncoding(), options.isXmlFiltering());
      }
    }
    prg.cleanUp();
  }

  private static void printLanguages() {
    List<String> languages = new ArrayList<>();

View on GitHub (pinned to 2e990059ce)

Solutions

1. Add --mother-tongue <sourceLanguageCode> alongside --bitext.
2. Ensure the source language code is a supported Language (e.g. en-US, de-DE).
3. If you do not actually want bitext checking, drop the --bitext flag.

Example fix

// before
languagetool -l de-DE --bitext --bitextrules rules.xml pair.txt
// after
languagetool -l de-DE --mother-tongue en-US --bitext --bitextrules rules.xml pair.txt

if (options.isBitext() && options.getMotherTongue() == null) {
  throw new IllegalArgumentException("--mother-tongue is required with --bitext");
}

try {
  prg.setBitextMode(motherTongue, disabled, enabled, bitextRuleFile);
} catch (IllegalArgumentException e) {
  printUsageAndExit("bitext mode requires --mother-tongue");
}

When it happens

Trigger: Running the CLI with --bitext (bitext rule file mode) but omitting --mother-tongue <lang>.

Common situations: New users assuming the target language (-l) suffices for bitext checking; scripts migrated from plain mode to bitext mode without adding the source-language flag.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• JSON output format is not implemented for Bitext
• Missing argument to <option> command line option.
• Parameter --config must be set and point to a property file
• Missing argument for '--logIpMatchingPattern' (e.g. any rand
• WrongParameterNumberException

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/3c73740fd3d29071. Report an issue: GitHub.