Fix bugs in main.py for English/German JSON conversion

[STACSEMTH]

Fix multiple bugs in "main.py" so that it correctly reads the input files, converts English/German sentence pairs into valid JSON lines, and writes the expected "concated.json" output.

1. "Fixed 'path_to_file_list' to actually read the file contents"
   In the original implementation, "path_to_file_list" opened the file in write mode ('w') and returned an undefined variable (lines), which erased the input file and raised a "NameError".
   Therefore, I changed it to open the file in read mode ('r') and return a list of lines (with trailing newlines stripped), so the function now correctly loads the input data.

2. "Corrected JSON escaping and template construction in 'train_file_list_to_json'"
   The original "process_file" function did not properly escape backslashes and used a condition (if '/' or ' " ' in file) that is always true.
   So, I replaced this logic with explicit replacements so that "\", "/", and """ are converted to "\\", "\/", and \" respectively.
   In addition, the JSON template previously used the "German" key twice and did not assemble a valid JSON string.
   I updated the template to produce {"English":"...","German":"..."} and now build each JSON line as
   "template_start + English + template_mid + German + template_end".

3. "Fixed file writing and main function flow"
   The original "write_file_list" opened the output file in read mode ('r') and only wrote newline characters, so no actual content was saved.
   So, I changed it to open the file in write mode ('w') and write each string from the list as a separate line.
   Finally, in "main", the functions were called with incorrect arguments: "train_file_list_to_json" was given a file path instead of two lists, and "path_to_file_list" was called with lists instead of a path.
   I updated "main" so that it (1) reads "english.txt" and "german.txt" using "path_to_file_list", (2) passes the two lists to "train_file_list_to_json", and (3) writes the resulting JSON lines to "concated.json" using "write_file_list".