diff --git a/__tests__/test.js b/__tests__/test.js
index 1f050fcb1..c43c3f8a9 100644
--- a/__tests__/test.js
+++ b/__tests__/test.js
@@ -193,6 +193,25 @@ describe("Universal Viewer", () => {
     expect(galleryViewAfterTwoUpToggle).toBe("hidden");
   });
 
+  it("labels gallery thumbnail size controls", async () => {
+    await page.waitForSelector(".iiif-gallery-component .size-down");
+
+    const labels = await page.$$eval(
+      [
+        ".iiif-gallery-component .size-down",
+        ".iiif-gallery-component input[type='range'][name='size']",
+        ".iiif-gallery-component .size-up",
+      ].join(", "),
+      (controls) => controls.map((control) => control.getAttribute("aria-label"))
+    );
+
+    expect(labels).toEqual([
+      "Decrease thumbnail size",
+      "Thumbnail size",
+      "Increase thumbnail size",
+    ]);
+  });
+
   it("settings button is visible", async () => {
     await page.waitForSelector(".btn.imageBtn.settings");
 
diff --git a/src/content-handlers/iiif/extensions/config/ContentLeftPanel.ts b/src/content-handlers/iiif/extensions/config/ContentLeftPanel.ts
index a7f2b46ae..38bfaeb3f 100644
--- a/src/content-handlers/iiif/extensions/config/ContentLeftPanel.ts
+++ b/src/content-handlers/iiif/extensions/config/ContentLeftPanel.ts
@@ -59,10 +59,13 @@ type ContentLeftPanelOptions = ExpandPanelOptions & {
 
 type ContentLeftPanelContent = ExpandPanelContent & {
   date: string;
+  decreaseThumbnailSize: string;
   index: string;
+  increaseThumbnailSize: string;
   manifestRanges: string;
   searchResult: string;
   searchResults: string;
+  thumbnailSize: string;
   sortBy: string;
   thumbnails: string;
   title: string;
diff --git a/src/content-handlers/iiif/extensions/uv-av-extension/config/config.json b/src/content-handlers/iiif/extensions/uv-av-extension/config/config.json
index 0a31683f1..7e4b09d99 100644
--- a/src/content-handlers/iiif/extensions/uv-av-extension/config/config.json
+++ b/src/content-handlers/iiif/extensions/uv-av-extension/config/config.json
@@ -91,12 +91,15 @@
         "collapse": "$collapse",
         "collapseFull": "$collapseFull",
         "date": "$date",
+        "decreaseThumbnailSize": "$decreaseThumbnailSize",
         "expand": "$expandContents",
         "expandFull": "$expandGallery",
         "index": "$index",
+        "increaseThumbnailSize": "$increaseThumbnailSize",
         "manifestRanges": "$manifestRanges",
         "searchResult": "$searchResult",
         "searchResults": "$searchResults",
+        "thumbnailSize": "$thumbnailSize",
         "sortBy": "$sortBy",
         "thumbnails": "$thumbnails",
         "title": "$contents",
diff --git a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/Config.ts b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/Config.ts
index 4a3df8ecd..ccd9adfd3 100644
--- a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/Config.ts
+++ b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/Config.ts
@@ -35,8 +35,11 @@ type MultiSelectDialogueOptions = DialogueOptions & {
 };
 
 type MultiSelectDialogueContent = DialogueContent & {
+  decreaseThumbnailSize: string;
   download: string;
+  increaseThumbnailSize: string;
   selectAll: string;
+  thumbnailSize: string;
   title: string;
 };
 
diff --git a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/config.json b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/config.json
index 5b3eb2145..bcf242d14 100644
--- a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/config.json
+++ b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/config/config.json
@@ -101,12 +101,15 @@
         "collapse": "$collapse",
         "collapseFull": "$collapseFull",
         "date": "$date",
+        "decreaseThumbnailSize": "$decreaseThumbnailSize",
         "expand": "$expandContents",
         "expandFull": "$expandGallery",
         "index": "$index",
+        "increaseThumbnailSize": "$increaseThumbnailSize",
         "manifestRanges": "$manifestRanges",
         "searchResult": "$searchResult",
         "searchResults": "$searchResults",
+        "thumbnailSize": "$thumbnailSize",
         "sortBy": "$sortBy",
         "thumbnails": "$thumbnails",
         "title": "$contents",
@@ -280,8 +283,11 @@
       },
       "content": {
         "close": "$close",
+        "decreaseThumbnailSize": "$decreaseThumbnailSize",
         "download": "$download",
+        "increaseThumbnailSize": "$increaseThumbnailSize",
         "selectAll": "$selectAll",
+        "thumbnailSize": "$thumbnailSize",
         "title": "$selectPagesForDownload"
       }
     },
diff --git a/src/content-handlers/iiif/modules/uv-shared-module/GalleryComponent.ts b/src/content-handlers/iiif/modules/uv-shared-module/GalleryComponent.ts
index b5fbe9eb3..20c29da04 100644
--- a/src/content-handlers/iiif/modules/uv-shared-module/GalleryComponent.ts
+++ b/src/content-handlers/iiif/modules/uv-shared-module/GalleryComponent.ts
@@ -12,8 +12,11 @@ import { BaseComponent, IBaseComponentOptions } from "@iiif/base-component";
 import { Strings, Maths } from "../../Utils";
 
 export interface IGalleryComponentContent {
+  decreaseThumbnailSize: string;
+  increaseThumbnailSize: string;
   searchResult: string;
   searchResults: string;
+  thumbnailSize: string;
   download: string;
   selectAll: string;
 }
@@ -60,6 +63,11 @@ export class GalleryComponent extends BaseComponent {
 
   constructor(options: IBaseComponentOptions) {
     super(options);
+    this.options.data.content = Object.assign(
+      {},
+      this.data().content,
+      this.options.data.content
+    );
     this._data = this.options.data;
     this._init();
     this._resize();
@@ -81,19 +89,19 @@ export class GalleryComponent extends BaseComponent {
 
     this._$sizeDownButton = $(
       '<input class="btn btn-default size-down" type="button" value="-" />'
-    );
+    ).attr("aria-label", this.options.data.content.decreaseThumbnailSize);
     this._$leftOptions.append(this._$sizeDownButton);
 
     this._$sizeRange = $(
       '<input type="range" name="size" min="1" max="10" value="' +
         this.options.data.initialZoom +
         '" />'
-    );
+    ).attr("aria-label", this.options.data.content.thumbnailSize);
     this._$leftOptions.append(this._$sizeRange);
 
     this._$sizeUpButton = $(
       '<input class="btn btn-default size-up" type="button" value="+" />'
-    );
+    ).attr("aria-label", this.options.data.content.increaseThumbnailSize);
     this._$leftOptions.append(this._$sizeUpButton);
 
     this._$multiSelectOptions = $('<div class="multiSelectOptions"></div>');
@@ -199,8 +207,11 @@ export class GalleryComponent extends BaseComponent {
     return {
       chunkedResizingThreshold: 400,
       content: <IGalleryComponentContent>{
+        decreaseThumbnailSize: "Decrease thumbnail size",
+        increaseThumbnailSize: "Increase thumbnail size",
         searchResult: "{0} search result",
         searchResults: "{0} search results",
+        thumbnailSize: "Thumbnail size",
       },
       debug: false,
       helper: null,
diff --git a/src/locales/cy-GB.json b/src/locales/cy-GB.json
index 349060930..c9171ee07 100644
--- a/src/locales/cy-GB.json
+++ b/src/locales/cy-GB.json
@@ -134,6 +134,9 @@
   "$shareLink": "Dolen i'r dudalen hon",
   "$shareInstructions": "Er mwyn rhannu'r eitem hon, cop\u00efwch y URL isod.",
   "$size": "Maint:",
+  "$decreaseThumbnailSize": "Lleihau maint bawdluniau",
+  "$thumbnailSize": "Maint bawdluniau",
+  "$increaseThumbnailSize": "Cynyddu maint bawdluniau",
   "$width": "Lled",
   "$cancel": "Canslo",
   "$confirm": "Cadarnhau",
diff --git a/src/locales/en-GB.json b/src/locales/en-GB.json
index 308c8c874..c23544922 100644
--- a/src/locales/en-GB.json
+++ b/src/locales/en-GB.json
@@ -134,6 +134,9 @@
   "$shareLink": "Link to this Page",
   "$shareInstructions": "To share this item, copy the URL below.",
   "$size": "Size:",
+  "$decreaseThumbnailSize": "Decrease thumbnail size",
+  "$thumbnailSize": "Thumbnail size",
+  "$increaseThumbnailSize": "Increase thumbnail size",
   "$width": "Width",
   "$cancel": "Cancel",
   "$confirm": "Confirm",
diff --git a/src/locales/fr-FR.json b/src/locales/fr-FR.json
index 6c0ec117c..e9821fb0d 100644
--- a/src/locales/fr-FR.json
+++ b/src/locales/fr-FR.json
@@ -133,6 +133,9 @@
   "$shareLink": "Un lien vers cette page",
   "$shareInstructions": "Pour partager ce contenu, copier l'URL ci-dessous.",
   "$size": "Taille :",
+  "$decreaseThumbnailSize": "Réduire la taille des vignettes",
+  "$thumbnailSize": "Taille des vignettes",
+  "$increaseThumbnailSize": "Augmenter la taille des vignettes",
   "$width": "Largeur",
   "$cancel": "Annuler",
   "$confirm": "Confirmer",
diff --git a/src/locales/pl-PL.json b/src/locales/pl-PL.json
index 3d6e5d180..ec011c814 100644
--- a/src/locales/pl-PL.json
+++ b/src/locales/pl-PL.json
@@ -133,6 +133,9 @@
   "$shareLink": "Link do tej strony",
   "$shareInstructions": "Aby udostępnić ten obiekt, skopiuj poniższy adres URL.",
   "$size": "Rozmiar:",
+  "$decreaseThumbnailSize": "Zmniejsz rozmiar miniatur",
+  "$thumbnailSize": "Rozmiar miniatur",
+  "$increaseThumbnailSize": "Zwiększ rozmiar miniatur",
   "$width": "Szerokość",
   "$cancel": "Anuluj",
   "$confirm": "Potwierdź",
diff --git a/src/locales/sv-SE.json b/src/locales/sv-SE.json
index 74dfb0c83..69f5c1658 100644
--- a/src/locales/sv-SE.json
+++ b/src/locales/sv-SE.json
@@ -133,6 +133,9 @@
   "$shareLink": "Länk till denna sida",
   "$shareInstructions": "Kopiera länken nedan för att dela det här objektet.",
   "$size": "Storlek:",
+  "$decreaseThumbnailSize": "Minska miniatyrstorlek",
+  "$thumbnailSize": "Miniatyrstorlek",
+  "$increaseThumbnailSize": "Öka miniatyrstorlek",
   "$width": "Bredd",
   "$cancel": "Avbryt",
   "$confirm": "Bekräfta",