i18n(ja): restore variable names and clean up heading anchors in system variable docs

[yahonda]

What is changed, added or deleted? (Required)

Japanese heading fixes for system-variable-reference.md and system-variables.md, in two parts:

1. Restore English system variable names in headings (original scope)

• system-variable-reference.md: 109 headings
• system-variables.md: 45 headings

2. Clean up heading anchors and version marks (follow-up)

The explicit {#...} anchors on English variable headings had converted underscores to hyphens (e.g. ### auto_increment_increment {#auto-increment-increment}), which does not match how the site auto-generates anchors (underscores are preserved) nor the underscore-form links used throughout the docs ([...](#auto_increment_increment)). As a result those cross-references were broken. Since the auto-generated anchor is already correct, the redundant {#...} anchors are removed.

For version-marked headings, the anchor only existed because New in vX.Y.Z had been translated into Japanese (e.g. vX.Y.Zで追加, or sentence forms leaving a stray は), which changed the auto-anchor. The version-mark text is restored to the English New in vX.Y.Z (matching the release-8.5 source) and the anchor is dropped. Two corrupted headings (zero-width spaces splitting a variable name, and an anchor that had captured the <span> markup) are also fixed.

Verification: all 84 same-file links and 1,642 repo-wide cross-file links into these two files resolve; no residual translated version marks, mangled anchors, or zero-width spaces remain.

This is a Japanese (ja) translation-only fix; no English source content is changed.

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)

What is the related PR or file link(s)?

• This PR is translated from: N/A (Japanese translation heading/anchor fix only)
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

Note on scope

A few of the lines in this PR also carry a fix that belongs to one of the sibling ja PRs. Where a later sweep found damage on a line this PR already edits, the fix was applied here rather than duplicated into another PR — otherwise the two PRs would conflict. So a small number of lines go beyond the scope stated above, for example:

-…発生します。1パラメータ`gc.max_write_bytes_per_sec`使用すると、…
+…発生します。`gc.max_write_bytes_per_sec`パラメータを使用すると、…

Here the stray 1 (a translation-tool placeholder) and the word order were repaired alongside this PR's particle insertion.

All fifteen ja PRs were verified to merge cleanly in any order (105 pairwise merges, 0 conflicts).

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[gemini-code-assist]

Code Review

This pull request updates the Japanese documentation files system-variable-reference.md and system-variables.md by replacing translated Japanese headings for system variables with their actual English system variable names (for example, changing '自動コミット' to 'autocommit'). This ensures consistency and technical accuracy across the reference documents. There are no review comments, and I have no feedback to provide.

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Timeline:

• 2026-07-29 14:08:10.244300315 +0000 UTC m=+2018676.280395371: ☑️ agreed by qiancai.