<PAGE>

                                                                 Exhibit 10.46

                      LOAN DOCUMENT MODIFICATION AGREEMENT
                     Number 6; dated as of December 20, 1999


      LOAN DOCUMENT MODIFICATION AGREEMENT dated as of December 20, 1999 (this
"Agreement") by and among SILICON VALLEY BANK (the "Bank"), a
California-chartered bank with its principal place of business located at 3003
Tasman Drive, Santa Clara, California 95054, and with a loan production office
located at 40 William Street, Wellesley, Massachusetts 02481, doing business
under the name "Silicon Valley East," LIONBRIDGE TECHNOLOGIES HOLDINGS B.V., a
company with limited liability, incorporated in the Netherlands and having a
principal place of business located at The Sinus Building, Overschiestraat 55,
1062 HN, Amsterdam, The Netherlands, LIONBRIDGE TECHNOLOGIES B.V., a company
with limited liability, incorporated in Netherlands and having a principal place
of business located at the same address (each a "Borrower" and collectively, the
"Borrowers") and LIONBRIDGE TECHNOLOGIES, INC., a Delaware company with its
principal place of business located at 950 Winter Street, Suite 2410, Waltham,
Massachusetts 02451 (the "Parent Guarantor").

      1. Reference to Existing Loan Documents.

      Reference is hereby made to that Loan Agreement dated as of September 26,
1997 among the Bank and the Borrowers, as amended by Loan Documentation
Modification Agreement No. 1 dated as of May 21, 1998, as further amended by
Loan Document Modification Agreement No. 2 dated as of February 25, 1999, Loan
Document Modification Agreement No. 3 dated as of May 20, 1999, Loan Document
Modification Agreement No. 4 dated as of July 16, 1999 and Loan Document
Modification Agreement No. 5 dated as of September 20, 1999 (with the attached
schedules and exhibits, and as the same may hereafter be further amended,
modified, supplemented, extended or restated from time to time, the "Loan
Agreement") and the Loan Documents referred to therein, including without
limitation that certain Amended and Restated Promissory Note of the Borrowers
dated as of September 20, 1999 in the principal amount of $8,000,000 (the
"Amended Note") and the Security Documents referred to therein, and also
including that certain Amended and Restated Guarantee of the Parent Guarantor
dated as of May 21, 1998 in favor of the Bank (the "Parent Guarantee"). Unless
otherwise defined herein, capitalized terms used in this Agreement shall have
the same respective meanings as set forth in the Loan Agreement.

      2. Effective Date.

      This Agreement shall become effective as of December 20, 1999 (the
"Effective Date"), provided that the Bank shall have received the following on
or before December 29, 1999 and provided further, however, in no event shall
this Agreement become effective until signed by an officer of the Bank in
California:

            a. two copies of this Agreement, duly executed by each Borrower and
the Parent Guarantor;

            b. an amended and restated promissory note in the form enclosed
herewith (the "Amended Note"), duly executed by the Borrowers;

<PAGE>

                                       -2-


            c. the attached consents of affiliated entities who have previously
furnished guaranties in favor of the Bank of the obligations of the Borrowers,
duly executed by officers thereof

            d. payment of the Bank's facility fee specified below; and

            e. such other documents, and completion of such other matters, as
the Bank may reasonably request in connection with the amendment of the Loan
Agreement, as contemplated hereunder.

      By the signature of its authorized officer below, the Borrowers are hereby
representing that, except as modified in Schedule A attached hereto, the
representations of the Borrowers set forth in the Loan Documents (including
those contained in the Loan Agreement, as amended by this Agreement) are true
and correct as of the Effective Date as if made on and as of such date. In
addition, the Borrowers confirm their authorization as to the debiting of their
account with the Bank in the amount of $ 10,000 in order to pay the Bank's
facility fee for the period up to and including the extended Revolving Maturity
Date. Finally, the Borrowers (and each guarantor signing below) agree that, as
of the Effective Date, they have no defenses against their obligations to pay
any amounts under the Loan Agreement and the other Loan Documents.

      3. Description of Change in Terms.

      As of the Effective Date, the Loan Agreement and the Parent Guarantee are
modified in the following respects:

            a. Section 1.1 of the Loan Agreement is hereby amended by restating
the definition of "Revolving Maturity Date" in its entirety as follows:

            "'Revolving Maturity Date' means March 20, 2000."

            b. Section 13(c) of the Parent Guarantee is hereby amended by (i)
decreasing the minimum EBITDA requirement for the fiscal quarter ended December
31, 1999 from ($1,000,000) to ($1,750,000) and (ii) setting the minimum EBITDA
requirement for the fiscal quarter ended March 31, 2000 at ($1,000,000).

            c. The Compliance Certificate attached to the Parent Guarantee is
amended by restating in its entirety Exhibit A thereto in the form of Exhibit A
hereto.

            d. The Loan Agreement and the other Loan Documents are hereby
amended wherever necessary or appropriate to reflect the foregoing changes.

      4. Continuing Validity.

      Upon the effectiveness hereof, each reference in each Security Instrument
or other Loan Document to (i) "the Loan Agreement," "thereunder," "thereof,"
"therein" or words of like import referring to the Loan Agreement, shall mean
and be a reference to the Loan Agreement, as amended hereby and (ii) "the Parent
Guarantee," "thereunder," "thereof," "therein" or words of like import referring
to the Parent Guarantee, shall mean and be a reference to the Parent

<PAGE>

                                       -3-


Guarantee, as amended hereby. Except as specifically set forth above, the Loan
Agreement shall remain in full force and effect and is hereby ratified and
confirmed.

      Each of the other Loan Documents is in full force and effect and is hereby
ratified and confirmed. The amendments and limited waiver set forth above (i) do
not constitute a waiver or modification of any term, condition or covenant of
the Loan Agreement or any other Loan Document, other than as expressly set forth
herein, and (ii) shall not prejudice any rights which the Bank may now or
hereafter have under or in connection with the Loan Agreement, as modified
hereby, or the other Loan Documents, and shall not obligate the Bank to assent
to any further modifications.

      5. Miscellaneous.

            a. This Agreement may be signed in one or more counterparts each of
which taken together shall constitute one and the same document.

            b. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
WITH THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS.

            c. THE BORROWERS ACCEPT FOR THEMSELVES AND IN CONNECTION WITH THEIR
PROPERTIES, UNCONDITIONALLY, THE NON-EXCLUSIVE JURISDICTION OF ANY STATE OR
FEDERAL COURT OF COMPETENT JURISDICTION IN THE COMMONWEALTH OF MASSACHUSETTS IN
ANY ACTION, SUIT, OR PROCEEDING OF ANY KIND AGAINST THEM WHICH ARISES OUT OF OR
BY REASON OF THIS AGREEMENT; PROVIDED, HOWEVER, THAT IF FOR ANY REASON THE BANK
CANNOT AVAIL ITSELF OF THE COURTS OF THE COMMONWEALTH OF MASSACHUSETTS, THEN
VENUE SHALL LIE IN SANTA CLARA COUNTY, CALIFORNIA.

            d. The Borrowers agree to promptly pay on demand all costs and
expenses of the Bank in connection with the preparation, reproduction, execution
and delivery of this Agreement and the other instruments and documents to be
delivered hereunder, including the reasonable fees and out-of-pocket expenses of
Sullivan & Worcester LLP, special counsel for the Bank with respect thereto.

                  [Remainder of page intentionally left blank.]

<PAGE>

                                       -4-


      IN WITNESS WHEREOF, the Bank and the Borrowers have caused this Agreement
to be signed under seal by their respective duly authorized officers as of the
date set forth above.


                                   Sincerely,

                                   SILICON VALLEY EAST, a Division
                                     of Silicon Valley Bank


                                   By:
                                       ---------------------------------------
                                             Andrew H. Tsao
                                             Senior Vice President

                                   SILICON VALLEY BANK


                                   By:
                                       ---------------------------------------
                                             Name:
                                             Title:
                                             (signed in Santa Clara, CA)

                                   BORROWERS:

                                   LIONBRIDGE TECHNOLOGIES HOLDINGS B.V.


                                   By: /s/ Rory J. Cowan
                                       ---------------------------------------
                                             Rory J. Cowan
                                             Managing Director

                                   LIONBRIDGE TECHNOLOGIES B.V.


                                   By: /s/ Rory J. Cowan
                                       ---------------------------------------
                                             Rory J. Cowan
                                             Managing Director

                                   PARENT GUARANTOR:

                                   LIONBRIDGE TECHNOLOGIES, INC.


                                   By: /s/ Rory J. Cowan
                                       ---------------------------------------
                                             Rory J. Cowan
                                             Title: