Perl-Application and queries with accented characters using postgres

Question

It's been a decade I have worked with Postgres and Perl.

One of my oldest still-operated applications, an dictionary of government addresses and departmental responsibilities, has issues handling query terms containing accented characters, for example köln. In other words, whenever a query term contains a accented character (mainly umlauts) there are 0 results returned.

I have to mention that this behavior is only happening using this application with Postgres as the database. If I switch to MySQL5 (same data) same queries are working correctly.

Trying to track the cause of this problem I have checked the following:

• Postgres database is UTF-8 (using the command show server_encoding;)
• Postgres client encoding is also UTF8 (using show client_encoding;)
• If I use the Postgres monitor and execute the same SQL query as the application does, using accented characters in the query term, I get correct results
• The Perl application itself is handling UTF-8, the HTML-Header is set correctly, contents of the output display correct and not garbled
• All Perl code files, scripts, .pm package files and templates are UTF-8 encoded (I verified that with file --mime perl_file_name)
• I fiddled with the database connection, setting $self->{dbh}->{pg_enable_utf8} = 1; or/and $self->{dbh}->do("SET CLIENT_ENCODING TO 'UTF8';"); or/and $self->{dbh}->do("SET NAMES 'UTF8';"); with no change
• I've updated the DBD::Pg module to version 3.6.2, no change.

So I am pretty much out of ideas what else to check or try to get Postgres fully working. Like mentioned in my intro, same application just using MySQL as database works flawlessly.

2 years ago the application was changed to handle UTF-8 data, I did not do the changes myself, but as far as I can see in the code (compared to the code in my GIT repo) its just the HTML UTF8-Header print "Content-type: text/html; charset=utf-8\n\n"; and a few unrelated template parts. Perhaps that change somewhere is the origin for all the problems but I don't know what esp. to adjust for Postgres.

The current Perl version is 5.22.1, using Apache/2.2.22 (Ubuntu). The vhost configuration is simple:

AddHandler cgi-script .cgi .pl
ScriptAlias /...abs-path-to-app.../cgi-bin/
<Directory "/...abs-path-to-app.../cgi-bin/">
     AllowOverride None
     Options +Indexes +ExecCGI +MultiViews +SymLinksIfOwnerMatch
     <IfVersion < 2.4>
         Allow from all
     </IfVersion>
     <IfVersion >= 2.4>
         Require all granted
     </IfVersion>
     Allow from all
</Directory>

Postgres is version 9.1.24.

Edit:

Collate and Ctype is set to en_US.UTF-8, Encoding is set to UTF-8 for the database in question. Taking a look into the tables, all character varying columns use pg_catalog."default" collation. Executing show lc_collate; show already mentioned en_US.UTF-8.

Edit2:

Using the DBD::Pg flag pg_enable_utf8 and setting it to 0 seems to work out and I get the expected results. Using a value other than 0, for example '-1or1` does not work. I tried out that flag (once again) right after the database connect. Actually I have to verify this as I still do not really understand what's going on.