On nightly build from l10n, javadoc generates English text.

Bundle: /net/disk1.sfbay/space0/crosscharge/j2se/1.5/ws/nightly/tiger_l10n_re/control/build/04-10-04/solaris-sparc/bundles/j2sdk-1_5_0-beta2-bin-l10n-nightly-solaris-sparc-10_apr_2004.sh

% locale
LANG=ja
LC_CTYPE="ja"
LC_NUMERIC="ja"
LC_TIME="ja"
LC_COLLATE="ja"
LC_MONETARY="ja"
LC_MESSAGES="ja"
LC_ALL=
%
% javadoc -J-showversion test.java
java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-l10n-nightly)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-l10n-master, mixed mode)
      :
%

See the following text in help-doc.html.

"Class" in header/footer
"All Classes" in header/footer

Package:
  "Classes"
  "Enums"
  "Exceptions"
  "Errors"
  "Annotation Types"

Class/Interface:
  "Nested Class Summary"
  "Field Summary"
  "Constructor Summary"
  "Method Summary"
  "Field Detail"
  "Constructor Detail"
  "Method Detail"

Annotation Type:
  (title itself)
  "Required Member Summary"
  "Optional Member Summary"
  "Member Detail"

Enum:
  (title itself)
  "Enum Constant Summary"
  "Enum Constant Detail"

Serialized Form:
  (title itself)

Constant Field Values:
  (title itself)