--- lbbs/src/editor.c	2025/11/08 08:21:31	1.55
+++ lbbs/src/editor.c	2025/11/09 11:18:07	1.57
@@ -77,6 +77,7 @@ EDITOR_DATA *editor_data_load(const char
 	long line_offsets[MAX_EDITOR_DATA_LINES + 1];
 	long current_data_line_length = 0;
 	long i;
+	int j;
 
 	if (p_data == NULL)
 	{
@@ -123,6 +124,15 @@ EDITOR_DATA *editor_data_load(const char
 		memcpy(p_editor_data->p_display_lines[i], p_data + line_offsets[i], (size_t)p_editor_data->display_line_lengths[i]);
 		current_data_line_length += p_editor_data->display_line_lengths[i];
 
+		// Convert \t to single space
+		for (j = 0; j < p_editor_data->display_line_lengths[i]; j++)
+		{
+			if (p_editor_data->p_display_lines[i][j] == '\t')
+			{
+				p_editor_data->p_display_lines[i][j] = ' ';
+			}
+		}
+
 		// Trim \n from last line
 		if (i + 1 == p_editor_data->display_line_total &&
 			p_editor_data->display_line_lengths[i] > 0 &&
@@ -647,9 +657,10 @@ int editor_display(EDITOR_DATA *p_editor
 	EDITOR_CTX ctx;
 	int ch = 0;
 	char input_str[5];
+	int str_len = 0;
 	wchar_t wcs[2];
+	int wc_len;
 	char c;
-	int str_len = 0;
 	int input_ok;
 	const int screen_begin_row = 1;
 	const int screen_row_total = SCREEN_ROWS - screen_begin_row;
@@ -1025,13 +1036,36 @@ int editor_display(EDITOR_DATA *p_editor
 					offset_in = split_line(p_editor_data->p_display_lines[line_current - output_current_row + row_pos],
 										   (int)col_pos - 1, &eol, &display_len, 0);
 					col_pos = display_len;
-					if (offset_in >= 1 && p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in - 1] < 0) // UTF8
+					if (offset_in > 0)
 					{
-						split_line(p_editor_data->p_display_lines[line_current - output_current_row + row_pos],
-								   (int)col_pos - 1, &eol, &display_len, 0);
-						if (display_len == col_pos - 2)
+						str_len = 1;
+						offset_in--;
+						if (p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] < 0 ||
+							p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] > 127) // UTF8
 						{
-							col_pos--;
+							while (offset_in > 0 &&
+								   (p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] & 0xc0) != 0xc0)
+							{
+								str_len++;
+								offset_in--;
+							}
+
+							if (str_len > 4)
+							{
+								log_error("Invalid UTF-8 data detected: str_len > 4\n");
+							}
+
+							if (mbstowcs(wcs, p_editor_data->p_display_lines[line_current - output_current_row + row_pos] + offset_in, 1) ==
+								(size_t)-1)
+							{
+								log_error("mbstowcs() error\n");
+							}
+							wc_len = (UTF8_fixed_width ? 2 : wcwidth(wcs[0]));
+
+							if (wc_len == 2)
+							{
+								col_pos--;
+							}
 						}
 					}
 					if (col_pos >= 1)
@@ -1062,15 +1096,41 @@ int editor_display(EDITOR_DATA *p_editor
 					offset_in = split_line(p_editor_data->p_display_lines[line_current - output_current_row + row_pos],
 										   (int)col_pos - 1, &eol, &display_len, 0);
 					col_pos = display_len + 2;
-					if (offset_in < p_editor_data->display_line_lengths[line_current - output_current_row + row_pos] &&
-						p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] < 0) // UTF8
+					if (offset_in < p_editor_data->display_line_lengths[line_current - output_current_row + row_pos])
 					{
-						split_line(p_editor_data->p_display_lines[line_current - output_current_row + row_pos] + offset_in,
-								   1, &eol, &display_len, 0);
-						if (display_len == 0)
+						str_len = 0;
+						if ((p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] & 0x80) ==
+							0x80) // head of multi-byte character
+						{
+							c = (char)(p_editor_data->p_display_lines[line_current - output_current_row + row_pos][offset_in] & 0xf0);
+							while (c & 0x80)
+							{
+								str_len++;
+								c = (c & 0x7f) << 1;
+							}
+
+							if (str_len > 4)
+							{
+								log_error("Invalid UTF-8 data detected: str_len > 4\n");
+							}
+
+							if (mbstowcs(wcs, p_editor_data->p_display_lines[line_current - output_current_row + row_pos] + offset_in, 1) ==
+								(size_t)-1)
+							{
+								log_error("mbstowcs() error\n");
+							}
+							wc_len = (UTF8_fixed_width ? 2 : wcwidth(wcs[0]));
+
+							if (wc_len == 2)
+							{
+								col_pos++;
+							}
+						}
+						else
 						{
-							col_pos++;
+							str_len = 1;
 						}
+						offset_in += str_len;
 					}
 					if (col_pos <= p_editor_data->display_line_widths[line_current - output_current_row + row_pos])
 					{