Looks like a botched install. You might drop the database, create a new one, doulbe check your config files and db permissions, then reinstall.

After finally getting the installation to go, the install (install/index.php?locale=en-US&action=newdb) creates a bunch of tables (T_locales is not listed) then tells me "Now you can log in with...", so I naively assume that I can.

Nope, no such luck:

MySQL error!

Table 'b2evolution.T_locales' doesn't exist(Errno=1146)

Your query:
SELECT loc_locale, loc_charset, loc_datefmt, loc_timefmt, loc_name, loc_messages, loc_priority, loc_enabled FROM T_locales ORDER BY loc_priority

grepping, this table name appears in 3 files:

FROM T_locales ORDER BY loc_priority';
$query = "REPLACE INTO T_locales ( loc_locale, loc_charset, loc_datefmt, loc_timefmt, loc_name, loc_messages, loc_priority, loc_enabled ) VALUES ";
/opt/b2evolution/blogs/b2evocore/_functions_locale.php
'T_locales' => $tablelocales ,
/opt/b2evolution/blogs/conf/_advanced.php
$DB->query( 'DROP TABLE IF EXISTS T_locales' );
/opt/b2evolution/blogs/install/_functions_delete.php

... but i don't see _functions_create.php in that list. ~create.php creates a evo_locales (according to my MySQL log), which is used here:

$tablelocales = 'evo_locales';
/opt/b2evolution/blogs/conf/_advanced.php

Some fun. Should I just create T_locales based on the definition of evo_locales? Change the delivered code?

My B2Evolution is 0.9.0.12

Did I miss the link for a bug database?

Allan