This is pretty much the jist of the errors I get. Using MCP6.2 and Forge 3.3.8.162

 

    ^

src\minecraft\net\minecraft\src\StringTranslate.java:170: error: ';' expected

    public boolean isUnicode()

                            ^

src\minecraft\net\minecraft\src\StringTranslate.java:178: error: illegal start of expression

    public String translateKey(String par1Str)

    ^

src\minecraft\net\minecraft\src\StringTranslate.java:178: error: ';' expected

    public String translateKey(String par1Str)

                              ^

src\minecraft\net\minecraft\src\StringTranslate.java:178: error: ';' expected

    public String translateKey(String par1Str)

                                             ^

src\minecraft\net\minecraft\src\StringTranslate.java:186: error: illegal start of expression

    public String translateKeyFormat(String par1Str, Object par2ArrayOfObj[])

    ^

src\minecraft\net\minecraft\src\StringTranslate.java:186: error: ';' expected

    public String translateKeyFormat(String par1Str, Object par2ArrayOfObj[])

                                    ^

src\minecraft\net\minecraft\src\StringTranslate.java:186: error: ';' expected

    public String translateKeyFormat(String par1Str, Object par2ArrayOfObj[])

                                                           ^

src\minecraft\net\minecraft\src\StringTranslate.java:186: error: not a statement

    public String translateKeyFormat(String par1Str, Object par2ArrayOfObj[])

                                                                          ^

src\minecraft\net\minecraft\src\StringTranslate.java:186: error: ';' expected

    public String translateKeyFormat(String par1Str, Object par2ArrayOfObj[])

                                                                            ^

src\minecraft\net\minecraft\src\StringTranslate.java:195: error: illegal start of expression

    public String translateNamedKey(String par1Str)

    ^

src\minecraft\net\minecraft\src\StringTranslate.java:195: error: ';' expected

    public String translateNamedKey(String par1Str)

                                   ^

src\minecraft\net\minecraft\src\StringTranslate.java:195: error: ';' expected

    public String translateNamedKey(String par1Str)

                                                  ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: illegal start of expression

    public static boolean isBidrectional(String par0Str)

    ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: illegal start of expression

    public static boolean isBidrectional(String par0Str)

           ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: ';' expected

    public static boolean isBidrectional(String par0Str)

                 ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: ')' expected

    public static boolean isBidrectional(String par0Str)

                                               ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: illegal start of expression

    public static boolean isBidrectional(String par0Str)

                                                       ^

src\minecraft\net\minecraft\src\StringTranslate.java:200: error: ';' expected

    public static boolean isBidrectional(String par0Str)

                                                        ^

77 errors

We'd need the full log to see if there were any patching issues, which it looks there were.

However, as 1.2.5 is old, we no longer support deving for it, so update to 1.3.2.