Index: common/include/wchar.h
===================================================================
--- common/include/wchar.h	(revision 696b405386c8f231d8955f78acc39dd81137ea5c)
+++ common/include/wchar.h	(revision 696b405386c8f231d8955f78acc39dd81137ea5c)
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2025 Jiří Zárevúcky
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _LIBC_WCHAR_H_
+#define _LIBC_WCHAR_H_
+
+#include <_bits/NULL.h>
+#include <_bits/WEOF.h>
+#include <_bits/mbstate_t.h>
+#include <_bits/size_t.h>
+#include <_bits/wchar_limits.h>
+#include <_bits/wchar_t.h>
+#include <_bits/wint_t.h>
+#include <stdarg.h>
+
+/* Forward declarations for types. */
+typedef struct _IO_FILE FILE;
+struct tm;
+
+/*
+ * Complete list of functions straight out of ISO/IEC 9899:2023 (N3096 draft).
+ * Only some of these are implemented, but keep all standard prototypes here
+ * for less pain in libposix etc.
+ */
+
+int fputws(const wchar_t *__restrict__, FILE *__restrict__);
+int fwide(FILE *, int mode);
+int fwprintf(FILE *__restrict__, const wchar_t *__restrict__, ...);
+int fwscanf(FILE *__restrict__, const wchar_t *__restrict__, ...);
+int mbsinit(const mbstate_t *);
+int swprintf(wchar_t *__restrict__, size_t, const wchar_t *__restrict__, ...);
+int swscanf(const wchar_t *__restrict__, const wchar_t *__restrict__, ...);
+int vfwprintf(FILE *__restrict__, const wchar_t *__restrict__, va_list);
+int vfwscanf(FILE *__restrict__, const wchar_t *__restrict__, va_list);
+int vswprintf(wchar_t *__restrict__, size_t, const wchar_t *__restrict__, va_list);
+int vswscanf(const wchar_t *__restrict__, const wchar_t *__restrict__, va_list);
+int vwprintf(const wchar_t *__restrict__, va_list);
+int vwscanf(const wchar_t *__restrict__, va_list);
+int wcscmp(const wchar_t *, const wchar_t *);
+int wcscoll(const wchar_t *, const wchar_t *);
+int wcsncmp(const wchar_t *, const wchar_t *, size_t);
+int wctob(wint_t);
+int wmemcmp(const wchar_t *, const wchar_t *, size_t);
+int wprintf(const wchar_t *__restrict__, ...);
+int wscanf(const wchar_t *__restrict__, ...);
+long int wcstol(const wchar_t *__restrict__, wchar_t **__restrict__, int);
+long long int wcstoll(const wchar_t *__restrict__, wchar_t **__restrict__, int);
+size_t mbrlen(const char *__restrict__, size_t, mbstate_t *__restrict__);
+size_t mbrtowc(wchar_t *__restrict__ pwc, const char *__restrict__, size_t, mbstate_t *__restrict__);
+size_t mbsrtowcs(wchar_t *__restrict__ dst, const char **__restrict__ src, size_t, mbstate_t *__restrict__);
+size_t wcrtomb(char *__restrict__, wchar_t wc, mbstate_t *__restrict__);
+size_t wcscspn(const wchar_t *, const wchar_t *);
+size_t wcsftime(wchar_t *__restrict__, size_t maxsize, const wchar_t *__restrict__, const struct tm *__restrict__ timeptr);
+size_t wcslen(const wchar_t *);
+size_t wcsrtombs(char *__restrict__ dst, const wchar_t **__restrict__ src, size_t, mbstate_t *__restrict__);
+size_t wcsspn(const wchar_t *, const wchar_t *);
+size_t wcsxfrm(wchar_t *__restrict__, const wchar_t *__restrict__, size_t);
+unsigned long int wcstoul(const wchar_t *__restrict__, wchar_t **__restrict__, int);
+unsigned long long int wcstoull(const wchar_t *__restrict__, wchar_t **__restrict__, int);
+wchar_t *fgetws(wchar_t *__restrict__, int, FILE *__restrict__);
+wchar_t *wcscat(wchar_t *__restrict__, const wchar_t *__restrict__);
+wchar_t *wcscpy(wchar_t *__restrict__, const wchar_t *__restrict__);
+wchar_t *wcsncat(wchar_t *__restrict__, const wchar_t *__restrict__, size_t);
+wchar_t *wcsncpy(wchar_t *__restrict__, const wchar_t *__restrict__, size_t);
+wchar_t *wcstok(wchar_t *__restrict__, const wchar_t *__restrict__, wchar_t **__restrict__);
+wchar_t *wmemcpy(wchar_t *__restrict__, const wchar_t *__restrict__, size_t);
+wchar_t *wmemmove(wchar_t *, const wchar_t *, size_t);
+wchar_t *wmemset(wchar_t *, wchar_t, size_t);
+wint_t btowc(int);
+wint_t fgetwc(FILE *);
+wint_t fputwc(wchar_t, FILE *);
+wint_t getwc(FILE *);
+wint_t getwchar(void);
+wint_t putwc(wchar_t, FILE *);
+wint_t putwchar(wchar_t);
+wint_t ungetwc(wint_t, FILE *);
+
+// TODO: In C23, these functions have generic macro definitions for correct
+//       const handling.
+wchar_t *wcschr(const wchar_t *, wchar_t);
+wchar_t *wcspbrk(const wchar_t *, const wchar_t *);
+wchar_t *wcsrchr(const wchar_t *, wchar_t);
+wchar_t *wcsstr(const wchar_t *, const wchar_t *);
+wchar_t *wmemchr(const wchar_t *, wchar_t, size_t);
+
+#endif /* _LIBC_WCHAR_H_ */
