See https://github.com/IHTSDO/snomed-scg-parser/blob/master/parser-generation/README.md to generate ANTLR4 from the ABNF grammar file. Name the generated file ECL.g4 and copy the file to the directory src/main/antlr4/org/snomed/langauges/ecl/generated/parser/.
In order to allow non-english language characters, the following lexer rule needs to be manually added to the ECL.g4 file (borrowed from the ANTLR4 lexer, https://github.com/antlr/grammars-v4/blob/master/antlr4/LexBasic.g4):
UTF8_LETTER
: '\u00C0' .. '\u02FF'
| '\u0370' .. '\u037D'
| '\u037F' .. '\u1FFF'
| '\u200C' .. '\u200D'
| '\u2070' .. '\u218F'
| '\u2C00' .. '\u2FEF'
| '\u3001' .. '\uD7FF'
| '\uF900' .. '\uFDCF'
| '\uFDF0' .. '\uFFFD'
;
Also, the following lines should be removed, if present:
utf8_2 : (U_00C2 | U_00C3 | U_00C4 | U_00C5 | U_00C6 | U_00C7 | U_00C8 | U_00C9 | U_00CA | U_00CB | U_00CC | U_00CD | U_00CE | U_00CF | U_00D0 | U_00D1 | U_00D2 | U_00D3 | U_00D4 | U_00D5 | U_00D6 | U_00D7 | U_00D8 | U_00D9 | U_00DA | U_00DB | U_00DC | U_00DD | U_00DE | U_00DF) utf8_tail;
utf8_3 : (U_00E0 (U_00A0 | U_00A1 | U_00A2 | U_00A3 | U_00A4 | U_00A5 | U_00A6 | U_00A7 | U_00A8 | U_00A9 | U_00AA | U_00AB | U_00AC | U_00AD | U_00AE | U_00AF | U_00B0 | U_00B1 | U_00B2 | U_00B3 | U_00B4 | U_00B5 | U_00B6 | U_00B7 | U_00B8 | U_00B9 | U_00BA | U_00BB | U_00BC | U_00BD | U_00BE | U_00BF) utf8_tail) | ((U_00E1 | U_00E2 | U_00E3 | U_00E4 | U_00E5 | U_00E6 | U_00E7 | U_00E8 | U_00E9 | U_00EA | U_00EB | U_00EC) ( utf8_tail ) (utf8_tail)) | (U_00ED (U_0080 | U_0081 | U_0082 | U_0083 | U_0084 | U_0085 | U_0086 | U_0087 | U_0088 | U_0089 | U_008A | U_008B | U_008C | U_008D | U_008E | U_008F | U_0090 | U_0091 | U_0092 | U_0093 | U_0094 | U_0095 | U_0096 | U_0097 | U_0098 | U_0099 | U_009A | U_009B | U_009C | U_009D | U_009E | U_009F) utf8_tail) | ((U_00EE | U_00EF) ( utf8_tail ) (utf8_tail));
utf8_4 : (U_00F0 (U_0090 | U_0091 | U_0092 | U_0093 | U_0094 | U_0095 | U_0096 | U_0097 | U_0098 | U_0099 | U_009A | U_009B | U_009C | U_009D | U_009E | U_009F | U_00A0 | U_00A1 | U_00A2 | U_00A3 | U_00A4 | U_00A5 | U_00A6 | U_00A7 | U_00A8 | U_00A9 | U_00AA | U_00AB | U_00AC | U_00AD | U_00AE | U_00AF | U_00B0 | U_00B1 | U_00B2 | U_00B3 | U_00B4 | U_00B5 | U_00B6 | U_00B7 | U_00B8 | U_00B9 | U_00BA | U_00BB | U_00BC | U_00BD | U_00BE | U_00BF) ( utf8_tail ) (utf8_tail)) | ((U_00F1 | U_00F2 | U_00F3) ( utf8_tail ) (utf8_tail) (utf8_tail)) | (U_00F4 (U_0080 | U_0081 | U_0082 | U_0083 | U_0084 | U_0085 | U_0086 | U_0087 | U_0088 | U_0089 | U_008A | U_008B | U_008C | U_008D | U_008E | U_008F) ( utf8_tail ) (utf8_tail));
utf8_tail : (U_0080 | U_0081 | U_0082 | U_0083 | U_0084 | U_0085 | U_0086 | U_0087 | U_0088 | U_0089 | U_008A | U_008B | U_008C | U_008D | U_008E | U_008F | U_0090 | U_0091 | U_0092 | U_0093 | U_0094 | U_0095 | U_0096 | U_0097 | U_0098 | U_0099 | U_009A | U_009B | U_009C | U_009D | U_009E | U_009F | U_00A0 | U_00A1 | U_00A2 | U_00A3 | U_00A4 | U_00A5 | U_00A6 | U_00A7 | U_00A8 | U_00A9 | U_00AA | U_00AB | U_00AC | U_00AD | U_00AE | U_00AF | U_00B0 | U_00B1 | U_00B2 | U_00B3 | U_00B4 | U_00B5 | U_00B6 | U_00B7 | U_00B8 | U_00B9 | U_00BA | U_00BB | U_00BC | U_00BD | U_00BE | U_00BF);
Then, all instances of utf8_2, utf8_3, utf8_4, and utf8_tail should be replaced with UTF8_LETTER. E.g.:
nonwsnonpipe : (EXCLAMATION | QUOTE | POUND | DOLLAR | PERCENT | AMPERSAND | APOSTROPHE | LEFT_PAREN | RIGHT_PAREN | ASTERISK | PLUS | COMMA | DASH | PERIOD | SLASH | ZERO | ONE | TWO | THREE | FOUR | FIVE | SIX | SEVEN | EIGHT | NINE | COLON | SEMICOLON | LESS_THAN | EQUALS | GREATER_THAN | QUESTION | AT | CAP_A | CAP_B | CAP_C | CAP_D | CAP_E | CAP_F | CAP_G | CAP_H | CAP_I | CAP_J | CAP_K | CAP_L | CAP_M | CAP_N | CAP_O | CAP_P | CAP_Q | CAP_R | CAP_S | CAP_T | CAP_U | CAP_V | CAP_W | CAP_X | CAP_Y | CAP_Z | LEFT_BRACE | BACKSLASH | RIGHT_BRACE | CARAT | UNDERSCORE | ACCENT | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | LEFT_CURLY_BRACE) | (RIGHT_CURLY_BRACE | TILDE) | utf8_2 | utf8_3 | utf8_4;
...becomes...
nonwsnonpipe : (EXCLAMATION | QUOTE | POUND | DOLLAR | PERCENT | AMPERSAND | APOSTROPHE | LEFT_PAREN | RIGHT_PAREN | ASTERISK | PLUS | COMMA | DASH | PERIOD | SLASH | ZERO | ONE | TWO | THREE | FOUR | FIVE | SIX | SEVEN | EIGHT | NINE | COLON | SEMICOLON | LESS_THAN | EQUALS | GREATER_THAN | QUESTION | AT | CAP_A | CAP_B | CAP_C | CAP_D | CAP_E | CAP_F | CAP_G | CAP_H | CAP_I | CAP_J | CAP_K | CAP_L | CAP_M | CAP_N | CAP_O | CAP_P | CAP_Q | CAP_R | CAP_S | CAP_T | CAP_U | CAP_V | CAP_W | CAP_X | CAP_Y | CAP_Z | LEFT_BRACE | BACKSLASH | RIGHT_BRACE | CARAT | UNDERSCORE | ACCENT | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | LEFT_CURLY_BRACE) | (RIGHT_CURLY_BRACE | TILDE) | UTF8_LETTER;
Finally, all instances of U_00xx : '\u00xx'; lexer rules can be deleted.