Docs: Update the "Translations" section in README

Make it clearer that translations cannot be accepted if they don't
come via the Translation Project.

Column headings have been handled automatically for years and now --help
is autowrapped too, so the related instructions can be removed.

README

@@ -10,6 +10,7 @@ XZ Utils
     2. Version numbering
     3. Reporting bugs
     4. Translations
+       4.1. Testing translations
     5. Other implementations of the .xz format
     6. Contact information
 
@@ -203,77 +204,47 @@ XZ Utils
 
         https://translationproject.org/html/translators.html
 
-    Below are notes and testing instructions specific to xz
-    translations.
+    Updates to translations won't be accepted by methods that bypass
+    the Translation Project because there is a risk of duplicate work:
+    translation updates made in the xz repository aren't seen by the
+    translators in the Translation Project. If you have found bugs in
+    a translation, please report them to the Language-Team address
+    which can be found near the beginning of the PO file.
 
-    Testing can be done by installing xz into a temporary directory:
+    If you find language problems in the original English strings,
+    feel free to suggest improvements. Ask if something is unclear.
+
+
+4.1. Testing translations
+
+    Testing can be done by installing xz into a temporary directory.
+
+    If building from Git repository (not tarball), generate the
+    Autotools files:
+
+        ./autogen.sh
+
+    Create a subdirectory for the build files. The tmp-build directory
+    can be deleted after testing.
+
+        mkdir tmp-build
+        cd tmp-build
+        ../configure --disable-shared --enable-debug --prefix=$PWD/inst
+
+    Edit the .po file in the po directory. Then build and install to
+    the "tmp-build/inst" directory, and use translations.bash to see
+    how some of the messages look. Repeat these  steps if needed:
 
-        ./configure --disable-shared --prefix=/tmp/xz-test
-        # <Edit the .po file in the po directory.>
         make -C po update-po
-        make install
-        bash debug/translation.bash | less
-        bash debug/translation.bash | less -S  # For --list outputs
+        make -j"$(nproc)" install
+        bash ../debug/translation.bash | less
+        bash ../debug/translation.bash | less -S  # For --list outputs
 
-    Repeat the above as needed (no need to re-run configure though).
+    To test other languages, set the LANGUAGE environment variable
+    before running translations.bash. The value should match the PO file
+    name without the .po suffix. Example:
 
-    Note especially the following:
-
-      - The output of --help and --long-help must look nice on
-        an 80-column terminal. It's OK to add extra lines if needed.
-
-      - In contrast, don't add extra lines to error messages and such.
-        They are often preceded with e.g. a filename on the same line,
-        so you have no way to predict where to put a \n. Let the terminal
-        do the wrapping even if it looks ugly. Adding new lines will be
-        even uglier in the generic case even if it looks nice in a few
-        limited examples.
-
-      - Be careful with column alignment in tables and table-like output
-        (--list, --list --verbose --verbose, --info-memory, --help, and
-        --long-help):
-
-          * All descriptions of options in --help should start in the
-            same column (but it doesn't need to be the same column as
-            in the English messages; just be consistent if you change it).
-            Check that both --help and --long-help look OK, since they
-            share several strings.
-
-          * --list --verbose and --info-memory print lines that have
-            the format "Description:   %s". If you need a longer
-            description, you can put extra space between the colon
-            and %s. Then you may need to add extra space to other
-            strings too so that the result as a whole looks good (all
-            values start at the same column).
-
-          * The columns of the actual tables in --list --verbose --verbose
-            should be aligned properly. Abbreviate if necessary. It might
-            be good to keep at least 2 or 3 spaces between column headings
-            and avoid spaces in the headings so that the columns stand out
-            better, but this is a matter of opinion. Do what you think
-            looks best.
-
-      - Be careful to put a period at the end of a sentence when the
-        original version has it, and don't put it when the original
-        doesn't have it. Similarly, be careful with \n characters
-        at the beginning and end of the strings.
-
-      - Read the TRANSLATORS comments that have been extracted from the
-        source code and included in xz.pot. Some comments suggest
-        testing with a specific command which needs an .xz file. You
-        may use e.g. any tests/files/good-*.xz. However, these test
-        commands are included in translations.bash output, so reading
-        translations.bash output carefully can be enough.
-
-      - If you find language problems in the original English strings,
-        feel free to suggest improvements. Ask if something is unclear.
-
-      - The translated messages should be understandable (sometimes this
-        may be a problem with the original English messages too). Don't
-        make a direct word-by-word translation from English especially if
-        the result doesn't sound good in your language.
-
-    Thanks for your help!
+        export LANGUAGE=fi
 
 
 5. Other implementations of the .xz format