diff --git a/src/ui/styles/cjk.css b/src/ui/styles/cjk.css
index 3c01d3987..d9cb9246d 100644
--- a/src/ui/styles/cjk.css
+++ b/src/ui/styles/cjk.css
@@ -1,6 +1,7 @@
-/* Tight tracking keeps Chinese labels readable; preserve Latin tracking for
-   intel HUD readouts and content marked translate="no", including its containers. */
-html:lang(zh)
+/* Chinese and Japanese text. Tight tracking keeps CJK labels readable;
+   preserve Latin tracking for intel HUD readouts and content marked
+   translate="no", including its containers. */
+html:is(:lang(zh), :lang(ja))
   body
   :not(
     #intel-hud,
@@ -12,40 +13,52 @@ html:lang(zh)
   letter-spacing: 0.02em !important;
 }
 
-/* Keep small Chinese labels legible at a minimum of 9px. */
-html:lang(zh) #command-dock .gev-mic-label,
-html:lang(zh) #command-dock #gev-voice-detail,
-html:lang(zh) .gev-voice-tier-btn,
-html:lang(zh) .panel-layer-toggle {
+/* Japanese line breaking: never start a line with ー, a small kana or closing
+   punctuation (プレビュ / ー). */
+html:lang(ja) body {
+  line-break: strict;
+}
+
+/* Keep small CJK labels legible at a minimum of 9px. */
+html:is(:lang(zh), :lang(ja)) #command-dock .gev-mic-label,
+html:is(:lang(zh), :lang(ja)) #command-dock #gev-voice-detail,
+html:is(:lang(zh), :lang(ja)) .gev-voice-tier-btn,
+html:is(:lang(zh), :lang(ja)) .panel-layer-toggle {
   font-size: 9px;
 }
 
 /* A two-glyph button label must not break between its glyphs. */
-html:lang(zh) .pp-mode-btn {
+html:is(:lang(zh), :lang(ja)) .pp-mode-btn {
+  white-space: nowrap;
+}
+
+/* Japanese segment labels are short words (すべて, 平面): keep each whole. */
+html:lang(ja) .gev-segment {
   white-space: nowrap;
 }
 
 /* Keep unit symbols in their catalog case, including the cockpit readouts. */
-html:lang(zh) #intel-hud *,
-html:lang(zh) #cockpit-hud * {
+html:is(:lang(zh), :lang(ja)) #intel-hud *,
+html:is(:lang(zh), :lang(ja)) #cockpit-hud * {
   text-transform: none;
 }
 
-/* Move short travel modes (步行 / 骑行) to the next line as whole words. */
-html:lang(zh) [data-layer-id='directions'] .data-toggle-meta {
+/* Move short travel modes (步行 / 骑行, 徒歩 / 自転車) to the next line as
+   whole words. */
+html:is(:lang(zh), :lang(ja)) [data-layer-id='directions'] .data-toggle-meta {
   word-break: keep-all;
   overflow-wrap: break-word;
 }
 
 /* Leave room for the complete sensor name and resolution on two lines. */
-html:lang(zh) .recent-imagery-readout .ri-strip {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-strip {
   height: 131px;
 }
-html:lang(zh) .recent-imagery-readout .ri-card {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-card {
   height: 123px;
   grid-template-rows: 42px 13px 22px 11px 18px;
 }
-html:lang(zh) .recent-imagery-readout .ri-card-sensor {
+html:is(:lang(zh), :lang(ja)) .recent-imagery-readout .ri-card-sensor {
   white-space: normal;
   text-overflow: clip;
 }