diff --git a/lang/si.css b/lang/si.css
new file mode 100644
index 0000000..e7533a8
--- /dev/null
+++ b/lang/si.css
@@ -0,0 +1,6 @@
+:lang(si) .theorem::before { content: 'ප්‍රමේය​යය ' counter(theorem) '. ' !important; }
+:lang(si) .lemma::before { content: 'උපසාධ්‍ය​ය ' counter(theorem) '. ' !important; }
+:lang(si) .proof::before { content: 'සාධන​ය ' attr(title) !important; }
+:lang(si) .definition::before { content: 'නිර්වචන​ය ' counter(definition) '. ' !important; }
+:lang(si) caption::before { content: 'වගු​ව ' counter(caption) '. ' !important; }
+:lang(si) figcaption::before { content: 'රූපසටහන ' counter(figcaption) '. ' !important; }
diff --git a/languages.html b/languages.html
index 5ea9d2f..ae681f3 100644
--- a/languages.html
+++ b/languages.html
@@ -53,6 +53,7 @@ <h5>Abstract</h5>
       <option value="pt">Portuguese (pt)</option>
       <option value="ro">Romanian (ro)</option>
       <option value="ru">Russian (ru)</option>
+      <option value="si">Sinhalese (si)</option>
       <option value="sl">Slovenian (sl)</option>
       <option value="sv">Swedish (sv)</option>
       <option value="tr">Turkish (tr)</option>